As a young man, Abraham Lincoln experienced bouts of despair so profound that friends were concerned he might commit suicide.

Ulysses S. Grant, the general under Lincoln who later rose to the presidency, often avoided social occasions and retreated into alcohol.

All told, almost half of American presidents from 1789 to 1974 had, suffered from a mental illness at some point in life, according to a recent analysis of biographical sources by psychiatrists at Duke University Medical Center. And more than half of those presidents, the study found, struggled with their symptoms -- most often depression -- while in office.

''What is hopeful about this is that it is evidence that people can suffer from depression or other mental problems and still function at a presidential level, if not at their best,'' said Dr. Jonathan Davidson, who, along with Dr. Kathryn Connor and Dr. Marvin Swartz, cataloged symptoms from presidential papers and biographies, and identified those disabling enough to qualify as disorders. They reported their findings in the current issue of The Journal of Nervous and Mental Disease.

The authors acknowledge the hazards and uncertainties of diagnosing from such a distance. But the lifetime rate of mental illness they found in these 37 presidents is identical to that found in some surveys of the American population.

In some cases, they included problems not usually thought of as mental disorders: William Howard Taft, the 27th president, for example, suffered from difficulty breathing while asleep -- most likely because of a disorder known as sleep apnea -- and often dozed off during important meetings.

In most cases the disorders recall the men: the indefatigable Theodore Roosevelt and Lyndon B. Johnson showed symptoms of the manic energy that characterizes bipolar disorder; Richard Nixon drank heavily through the Watergate period; and Calvin Coolidge plunged into a pit of depression after his teenage son died of an infection.

The report also serves as a caution against judging troubled souls too early. ''To contemporaries well acquainted with Madison, Hayes, Grant and Wilson,'' the authors write, ''it must have appeared that, as young men, these individuals were doing very little with their lives.'' BENEDICT CAREY