A research institute in Cambridge, Mass., has received $120,646 to investigate "the impact of home environment" on adolescent sexual activity. The Rand Corp. in Santa Monica, Calif., has been awarded $143,868 to explore the extent to which parental supervision affects a child's likelihood of having sex before marriage.

And at the University of Michigan's Institute for Social Research, a team of researchers will receive $77,984 to determine, among other things, why teen-agers have sex in their homes.

These and nine other federal grants totaling $1.2 million were made last fall under the Adolescent Family Life program, the federal government's new campaign to curb sex among teen-agers. In the words of its authorizing legislation, the program is supposed to fund research into the "societal causes and consequences of adolescent premarital sexual relations."

Skeptics wonder about the need to spend federal funds investigating the causes of premarital sex, but researchers insist there is much to learn.

Arland D. Thornton at the University of Michigan says his team, with earlier federal awards from the National Institutes of Health, has spent years interviewing more than 1,800 parents and children about their attitudes regarding sex.

Once Congress created the Adolescent Family Life program, Thornton found a new agency from which to seek federal support. One of the social research institute's earlier findings, he said, is that "many teen-agers report they are having sex at their homes."

"I think what's going on is that children are finding vacant homes and their children have enough confidence to have sex without their parents knowing about it . . . . This is opposed to old stereotypes, such as cars."

Thornton said the data could help shape "educational programs" but noted that there is much work to be done.