For about a decade now, educators have been noticing -- and worrying about -- a growing gender gap among college students, 57 percent of whom are female.

Among high-school seniors, women are more likely to have the ambition to go to college, to enroll, and then to do well, according to Education Department data. But much of the attention of those concerned about these figures has focused on subsets of the undergraduate population where the gender gap showed up most quickly and most dramatically.

Community colleges have reported severe gender gaps for years, which is consistent with studies showing that the gap in college-going rates is greatest among low-income students. The gender gap is quite large among black students, leading to significant gender gaps at historically black colleges, and in black enrollments at other institutions. And liberal arts colleges have struggled with the issue for years, with all sorts of theories about why men prefer to go elsewhere.

Now, evidence is emerging that the gender gap is extending as well to flagship public universities, some of which have not had to deal with the issue. At the University of North Carolina at Chapel Hill last week, some trustees were stunned to learn that the freshman class was 58 percent female. Some trustees suggested that the university consider some form of affirmative action for men, though the university doesn't plan to do so.

Some flagship public universities remain relatively equal in terms of undergraduates. The University of Michigan at Ann Arbor and the University of Maryland at College Park, for example, typically have 51-49 splits or 50-50 splits (and have similar figures this year).

But Chapel Hill isn't the only public facing the issue. While the university is still adjusting statistics, it appears that the next freshman class at the University of Virginia will be 56 percent female, up from 54 percent the previous year. The last time women made up no more than 51 percent of the student body there was 1991, and until 1980 women were in the minority. At the University of California this year (system wide), 57 percent of California residents admitted as freshmen were women.

At North Carolina, it fell to Jerry Lucido, vice provost for admissions and enrollment management, to explain to trustees why affirmative action for men is not the answer.

Lucido said that he thinks many flagships have been immune to the gender gap because they have large engineering programs that have substantial majorities of male students. He said that institutions like Chapel Hill that do not have engineering programs and have "more of a liberal arts orientation" will see the same issues liberal arts colleges have had.

"I'm really not surprised by the numbers," Lucido said, adding that Chapel Hill does not use gender as a factor in admissions decisions.

He cited a number of reasons why trustees and others are concerned. "They wonder about the social environment, and about the future of alumni giving. They are looking at all of the angles," he said.

Lucido also said that the issue is difficult at Chapel Hill and elsewhere because trustees remember their own college experience as having the opposite sort of gender gap.

Linda Sax, an associate professor of higher education at the University of California at Los Angeles, said that the Chapel Hill discussions illustrate the need for much more research on the gender gap, including questions of whether the gap is greater at some types of institutions. "There really is not yet a clearly defined explanation or a research agenda," she said.

Sax said that given the size and duration of the gender gap, it's also time for more study of its impact. "What is the impact on the campus environment, on women's experience, on men's experience?" Sax asked. "And what is the lasting impact on society of having a better educated female population?"