CHICAGO (AP) _ Reseachers who spent six years observing a group of high school valedictorians found that the women were much more likely than men to lower their career goals after college to pay attention to families.

The University of Illinois study followed 80 Illinois valedictorians, 46 women and 34 men, who graduated in 1981. Only 35 percent of the women now plan to stay in the labor force full-time, while all of the men do, researchers said.

''We're losing the talents of some of our best women,'' said Karen Arnold, who co-wrote the study with educational psychologist Terry Denny. ''The juggling of career and family seems to account for the women having lower career aspirations than the men.''

The women began to lower their career aspirations by the second year of college, said the researchers. By midway through college, the women studied also had lower levels of intellectual self-esteem and less ambitious goals than when they graduated from high school.

A Northwestern University education professor said the study shows women still must strive to become equal in the working world.

The women's movement has enjoyed ''public relations'' success, but substantive changes still are needed, said Joyce Van Tassel-Baska.

''What concerns me is the lowered expectations of women,'' she said. ''It's a waste of an incredible talent pool.''

Laura Kaufman, program director of the Chicago chapter of the National Organization for Women, said attitudes about the role of women in society must be changed.

''The reason the women in the study scaled back their expectations is because society hasn't changed enough to allow them to have both their career and family ambitions,'' Ms. Kaufman said.

Many young women still seem ready to reduce their own career goals for family considerations, said Jean Marie Linhart, this year's valedictorian at Oak Park-River Forest High School.

But Miss Linhart said she does not share the attitude of many of her classmates.

''Most of my friends have planned their careers, but if it comes down to the need to compromise, I think the women will still do the compromising,'' she said.

Miss Linhart said she plans to attend the University of Chicago and to pursue a career.

''To put it bluntly, I plan to change things,'' she said. ''Sure, he (a husband) can have his career as long as I get to do mine. It's a two-way street.''