Who is the addict? With addictive tragedies striking every community in the nation - with many millions of Americans addicted to alcohol and drugs alone - legions of scientists are asking: What aspects of psychological makeup contribute to addiction? Are there common threads that weave through all addictions, from hard drugs to cigarettes, from gambling to overeating?

It is part of a much broader effort that has already seen progress in understanding the chemistry of addiction, as biochemists isolate the chemicals and mechanisms by which the brain gives itself pleasure. And the whole panoply of addiction research has led to insights that buttress a profusion of therapies. Though some of them hold great promise, all would benefit from an increased understanding of the addictive personality.

Despite the wide gulf between an addiction to drugs and an addiction to gambling, some mental health experts find it useful to view addiction as including all self-destructive, compulsive behaviors. Some even go so far as to include the relatively benign activity of compulsive television-watching.

In bringing together much of the existing knowledge on the personality's role in addictions, with an emphasis on drugs and alcohol, a new study prepared for the National Academy of Sciences concludes that there is no single set of psychological characteristics that embrace all addictions. But the study does see common elements from addiction to addiction.

The report finds that there are several ''significant personality factors'' that can contribute to addiction:

- Impulsive behavior, difficulty in delaying gratification, an antisocial personality and a disposition toward sensation seeking.

- A high value on nonconformity combined with a weak commitment to the goals for achievement valued by the society.

- A sense of social alienation and a general tolerance for deviance.

- A sense of heightened stress. This may help explain why adolescence and other stressful transition periods are often associated with the most severe drug and alcohol problems.

The author of the study, Alan R. Lang, a psychology professor at Florida State University, believes that the continuing search for the personality traits that play a part in the development of addictions is an essential part of the broader fight against addiction, an opinion shared by others familiar with the field. ''If we can better identify the personality factors,'' he said in an interview, ''they can help us devise better treatment and can open up new strategies to intervene and break the patterns of addiction.''

Moreover, Dr. Lang believes that the insights provided by this kind of research could lead to much more effective preventive programs than those available today, to be used ''before problems reach the critical stage.'' Supplementing the personality factors listed in the academy's report, other behavioral scientists who have studied addicts point to additional often-found features of personality or background - a lack of self-esteem, marked depression or anxiety, physical or sexual abuse in childhood, and sharply conflicting parental expectations. The Inclusive Approach

The broad approach to addiction is taken by Lawrence J. Hatterer, an associate clinical professor of psychiatry at the Cornell University Medical College who wrote in his book, ''The Pleasure Addicts'' (Barnes) that ''Addictive behavior has invaded every aspect of American life today. We all feel the cloud of concern about becoming addictive - preoccupation with weight, smoking, drinking too much, or being caught in an excess of spending, acquiring, gambling, sex or work.''

Among other activities which, done in excess, have been characterized as addictive behavior are caffeine consumption, eating of chocolates or other sugar-laden foods, television watching, playing video games and even running.

But not all addictions are equally harmful and not all behavior that could lead to addiction necessarily does. Although Dr. Hatterer is among those who argue that addictions of all kinds are similar, he finds it useful to classify the abuse of alcohol, barbiturates and narcotics as ''hard addictions'' because of the quickness with which such substances affect many aspects of behavior, and adversely influence many people around the abuser. Dr. Hatterer terms compulsive behavior such as excessive smoking, gambling, running, spending or work as ''soft addictions'' because the consequences are not immediately felt by the abuser.

None of these activities are considered to be addictions by Dr. Hatterer unless they involve excessive, repetitive use of pleasurable activities to cope with unmanageable internal conflict, pressure and stress. While such activity may begin pleasurably in a person's life, the process in the addict involves increasing activity to achieve the same effect and eventually results in injury to the person's health or to his work, family and social relationships. The addicted person typically denies that his activity is detrimentally affecting him. If the addict is forced to stop, he finds he suffers physical or psychological withdrawal pains, and often feels compelled to resume his excessive pattern. Compulsiveness Is a Key

Moderation is the distinguishing characteristic. Most drinkers do not become alcoholics, and most runners do not become running addicts. However, if the runner is compulsively using his activity to cope with unresolved internal conflicts to the extent that he keeps injuring his body or destroying his work and family relationships, then he too has fallen victim to addictive behavior. He has become so dependent on the physical ''high'' he gets from his allencompassing running that he cannot concern himself with the difficulties it is causing.

Seeing common features in compulsive behavior, the national academy's Committee on Substance Abuse and Habitual Behavior has recently explored dependence on opiates, alcohol, smoking, overeating, gambling and television watching.

The committee report, to be published in February, contains the section on the addictive personality by Dr. Lang. He based his review largely on studies of alcohol and drug abusers, the areas in which the preponderance of research has been done. On the basis of these studies and his own research, Dr. Lang concluded that ''there is no single, unique personality entity that is a necessary and sufficient condition for substance use.'' Same Drug, Different Addictions

Reasons for this include the fact that the same drug can affect people differently and that drugs fulfill various needs for different people. Among alcohol abusers, for instance, the academy's report found that research had focused on two types: first, the anxious, depressed neurotic who may drink to kill his psychological pain; second, the unstable antisocial personality who drinks for excitement or sensation-seeking.

Although Dr. Lang's contribution emphasized alcohol and drugs, the rest of the report did not shy away from insights into addictive behavior involving television-watching and overeating. According to Charles P. O'Brien, a committee member and chief of psychiatry and head of the addiction research center at the Veterans Administration Medical Center in Philadelphia, the academy committee found that different types of addicts ''resemble each other in various ways.''

Dr. O'Brien said that people in all these addictions progressively needed greater quantities of stimulation to satisfy their needs and developed symptoms of withdrawal when deprived of the addictive activity. He also noted that addicts to one activity would often switch to another when deprived of opportunity to participate in the original addiction.

Dr. O'Brien said there are very important similarities in the personality characteristics of the addictions studied, including tendencies to depression, dependent behavior and difficulty in formulating long-term personal goals because of a concentration on short-term goals.

While personality plays a significant part in addictive behavior, behavioral scholars often note that addictions are a product of the subtle interplay between social factors and psychological factors, as well as the physiological components - and an understanding of the precise mix remains elusive. Switching Addictions

Certainly the availability of drugs, and social and legal attitudes toward them, play important roles in whether addictions develop and continue. For instance, research on veterans addicted to heroin in Vietnam indicated that only about eight percent of them continued the addiction after returning to the United States. But many of those who stopped using heroin had troubles when they returned home with a drug more widely available in the United States, alcohol. This observation lends support to those who see personality traits playing a part in crossing over from one addiction to another.

Drug availability and occupational stress help explain why ''physicians have the highest rate of opiate addiction of any group,'' according to Dr. O'Brien. He also notes that physicians have high rates of abuse of alcohol and mood-altering prescription drugs. Charles Winick, a sociologist at the City College of New York, has also linked availability and stress to high rates of drug dependence among physicians, particularly psychiatrists and surgeons.

Since most people do not become addicts, what is known about the ''non-addict'' profile? Dr. Robert B. Millman, director of the Alcohol and Drug Abuse Service at the Payne Whitney Psychiatric Clinic at the New York Hospital describes the best candidates for this group as ''those people who have strong families, often with religious backgrounds and who have good social relations.'' Experts say that the youth who has positive relations with his peers and with adults is less likely to fall prey to drug addiction than the antiauthoritarian loner who is achieving below his potential.

Although no one can say with certainty which kind of family is most likely to produce an addict, many mental health experts have strong views on the subject. For instance, Leon Wurmser, a psychiatry professor and former director of the Alcohol and Drug Abuse Program at the University of Maryland School of Medicine, notes that the potentially addictive child may well have been physically abused by parents, who are often themselves dependent on drugs or alcohol. He notes that the child has often been lied to, shamed and humiliated by parents who act in a highly inconsistent manner.

''The mother may support something that the father strongly disapproves, or a parent may tell the child one thing today and the opposite tomorrow,'' he says.

This legacy of brutality ''leaves the child in a helpless rage,'' Dr. Wurmser says. He does not view authority, which has been represented by the parents, as something which should be respected, but as capriciously cruel. The child can feel completely out of control and is racked by feelings of violence toward those around him. For him, the use of narcotics can be a way of trying to suppress the highly aggressive feelings that have resulted from his early trauma.

Dr. Hatterer agrees that cruelty to children often contributes to later addiction; he says that most of the addicts of all kinds that he has seen in his practice have been physically abused as children. Dr. Hatterer also shares Dr. Wurmser's view that inconsistent parental behavior shapes many addictive persons. Dangers of Inconsistency

''Every addictive adult I have treated has told either of excesses or inconsistencies or of deprivation or overindulgence in early life. There were shifts from too much to too little love, protection or discipline,'' Dr. Hatterer has written. There were also frequent instances of ''marked swings from unrealistic praise to destructive hypercritical behavior.''

While behavioral scientists agree that the addiction problem is one of great breadth and depth, some point out that concern about all potentially addictive substances can be misplaced. For instance, Dr. Lang, the author of the academy study on the addictive personality, wrote that some of the evidence he surveyed ''suggested that total abstinence from alcohol may indicate rigidity of personality structure as maladaptive as problem drinking itself.''

Next week: the chemistry of addiction.