A book by the Urban Institute challenges theories that increases in divorce and in the employment of mothers outside the home are the major cause of teenage drug use, suicide, high school dropouts, murder and poorer school performance.

The book, "The Changing American Family and Public Policy," also disputes the notion that the level of welfare benefits has a major impact on teenage pregnancy and family breakup.The book is another salvo in a long-standing dispute over what has caused some of the unfavorable social trends of recent decades. In effect, it challenges the idea that a return to the "traditional family," in which the mother stays home, would reverse most of the trends.

In one chapter, authors Frank Furstenberg Jr. and Gretchen Con-dran noted that the employment of mothers outside the home has been rising continuously for a generation and divorce has also been increasing rapidly.

During the the 1970s, according to their figures, almost all the statistics on scholastic aptitude scores, high school graduation rates, drug use, delinquency, homicide rates among teenagers, teenage suicide, birth rates among unmarried women, alcohol use and some other similar social indicators of teenage behavior got worse.

But in the late 1970s and early 1980s, they said, these unfavorable social statistics leveled off or began to improve, although women's employment outside the home was continuing to rise.

Divorce rates did level off in this later period as well, but this occurred too late to have much effect on those who were teenagers in the late 1970s and early 1980s, they said.

The authors said these figures suggest there is no direct correlation between female employment and many of the unfavorable trends. They say this thesis is reinforced by the finding that the same trend - with social statistics getting worse in the 1970s and improving in the early 1980s - is also apparent for higher age groups who would have been far less touched in their formative years by increase in divorce and mothers' employment.

Similar patterns were also found in Europe, the authors said.

The authors said the worsening of social indicators in the 1970s may have had major causes other than divorce and female employment.

One possible explanation, they said, is that "the Vietnam war precipitated a cultural crisis that sent shock waves through a number of institutions." Another is "public support for liberalizing prohibitions against drug use, certain sexual be-haviors and divorce."

Still a third is that competition within the huge Baby Boom generation for school places and jobs produced "generational conflict and youth alienation."

The authors said their findings strongly suggest that "in the unlikely event that parents . . . restored the `traditional family,' we seriously doubt that levels of drug use, alcohol consumption or crime would return" to the low levels of the 1950s.

Another chapter by Mary Jo Bane and Paul Jargowsky looks at national statistics and concludes that "policies like welfare, child care, tax credits and so on are not important determinants of trends in marriage, fertility or the formation of single-parent families."

For example, they said, the argument has been made that welfare, by allowing a woman to receive support even though she lacks the traditional source of family support, a husband, "rewards child-bearing outside marriage and family breakup. It also rewards, in the form of higher benefits, having additional children while unmarried."

The authors said that if welfare were a prime cause of inducing women to have children without husbands present, then the growth of female-headed families should have slacked off in the late 1970s and early 1980s when the real value of maximum welfare payment was dropping 33 percent in the average state because of inflation. However, the growth of female-headed families continued, suggesting other causes than trends in welfare benefits.

Similarly, they argued, if welfare causes family breakup, states with the highest welfare benefits should have the highest rates of family breakup, but "many of the states with the lowest benefits have the highest fraction of children living in female-headed families."