Women are twice as likely as men to suffer from major depression, and the reasons are less biological than cultural, according to a three-year study released yesterday.

Poverty, unhappy marriage, reproductive stress, and sexual and physical abuse are stronger factors than biology in accounting for the difference in depression rates between men and women, a research group for the American Psychological Association said.

Depression afflicts about 7 million American women, leads to 30,000 suicides annually and costs society an estimated $16 billion a year, the researchers said. The illness has been known for some time to strike women disproportionately, but interpreting this difference has been controversial, with some experts claiming that women simply are quicker to report emotional distress and more willing than men to seek treatment.

"This argument says women are not really more depressed, they just say and think so," said Ellen McGrath, director of the Psychology Center in New York and chairman of the research group. But evidence gathered by the researchers suggested that the sexual differences in the incidence of depression were real and that the particular problems facing women have been unappreciated by the medical profession.

"The task force found that women truly are more depressed than men primarily due to their experience being female in our contemporary culture," she said.

"Women are doubly disadvantaged," said University of Texas psychiatrist Jean Hamilton, one of the principal authors of the report. "Not only do we suffer twice as much depression as men, but special issues that complicate our depressions are often unappreciated, leading to under- treatment or overtreatment."

Mental health experts, however, cautioned that the findings should not be considered a definite answer to the puzzle of why women suffer greater emotional distress than men.

"The truth is that we don't know the answer," said Alan Leshner, acting director of the Alcohol, Drug Abuse and Mental Health Administration. "Depression is a complex psychobiological phenomenon. Women develop mood changes -- sometimes very severe mood changes -- accompanying changes in their reproductive status. They are pervasive enough that it gives one cause to believe that these are real biologically related phenomenon. But we also know that women are treated differently by society, and because of that it is quite likely that the differences are not entirely due to physiology. . . . What we don't know is how large the cultural component is."

The task force's principal finding is that no single factor is responsible for the dramatically higher rates of major depression among women. Nor, the report said, is the difference due entirely to simple biological differences between men and women. In fact, menstruation, pregnancy, abortion and menopause were found to be only modestly associated with severe emotional distress.

Infertility, however, was a major risk factor, with 40 percent of women in one study reporting that their inability to conceive was "the most upsetting experience of their lives."

Other key risk factors for women identified by the report were:

Cognitive and personality styles. Women are more prone to avoidant, passive, dependent behavior patterns and pessimistic, negative thought processes and are more likely than men to focus on depressed feelings rather than developing "action and mastery strategies."

Marriage and children. Married women are three times more likely than either married men or single women to be depressed in an unhappy marriage, with vulnerability to depression increasing as the number of children increases and the age of the children decreases. Women with more and younger children are more depressed than those with fewer and older children.

Sexual and physical abuse. New evidence suggests that victimization of women may be more prevalent than previously thought, and, as a result, may play an underappeciated role in promoting depression.

Poverty. Women in low-income groups are at significantly greater risk for depression, and 75 percent of those below the poverty line in the United States are women and children.

"I agree that these are significant risk factors for depression," said Leshner. "But there are a variety of other factors as yet unidentified that must be identified, whether psychosocial or biological or a combination."