A gap in pay between U.S. college-educated men and women starts soon after graduation and widens over time, according to a study released yesterday.

One year after receiving degrees, women working full time already earned 20 percent less than men, a report from the American Association of University Women found. The difference grew to about 30 percent a decade after graduation.

Not all the gap can be explained by factors known to affect wages, such as gender occupational differences or child-rearing responsibilities, the report said. About a quarter of the difference in earnings remains even when comparing men and women with similar jobs and family situations.

"Relatively small gaps out of college are something to be concerned about," Catherine Hill, research director for the project, said in an interview. "Our study points to the continuing persistence of discrimination as a problem in the workplace."

Other studies have shown that the divide in earnings may have widened over the last 10 years.

In 2005, college-educated women between the ages of 36 and 45 earned about 74.7 cents an hour for every dollar earned by men of the same age and education, down from 75.7 cents a decade earlier, according a report by the Economic Policy Institute, a Washington research group funded partly by labor organizations.

The AAUW used data from a study by the U.S. Department of Education's National Center for Education Statistics called Baccalaureate and Beyond. It covered graduating classes from 1993 and 2000 and included full- and part-time workers, as well as some who had left the labor force.

One year after graduation, women made more than men in just one field, engineering, and made at least 90 percent as much in four others, according to a breakdown of findings for 10 professions. Pay in the five remaining disciplines ranged from 75 percent to 88 percent of men's salaries.

A decade after earning degrees, female engineering majors made 93 percent as much as men and in no profession did college-educated women's salaries surpass men's, according to the study.

"Part of this, we know, is probably gender discrimination," said Sylvia Allegretto, an economist at the Economic Policy Institute who had not yet seen the AAUW study. "But there's also the idea that women are less tied to the labor market."

For example, women predominantly took jobs considered more "family-friendly," such as teaching, yesterday's report showed. Ten years out of college, women also were more likely than men to be working part time, especially if they had children.

The AAUW report said federal and state policy makers should extend the Family and Medical Leave Act of 1993 to provide paid maternity and paternity leave to women and men. More men would then be encouraged to take advantage of the program, diminishing one major gender-based difference in the workplace.

Other recommendations included encouraging women to become more interested in male-dominated fields, such as engineering and mathematics. Universities and professional organizations also should show women how to negotiate for better positions and salaries, the report said.

Some government data do show that women have made progress over time, the AAUW's Hill said.

According to Census Bureau statistics released last year, the pay gap for full-time workers at all education levels was the narrowest ever, with women earning 77 cents for every dollar paid to men. Education Department figures show the share of women attending college rose to 51 percent in 2003, from 33 percent three decades earlier.