Women comprised only 21 percent of the academics who accepted tenure-track offers to join the Faculty of Arts and Sciences (FAS) last year, a startling reversal of a three-year trend that saw that figure rise to 40 percent in 2004-2005.

It’s too soon to tell whether the sheer one-year drop, identified in the first annual FAS report on diversity, represents an anomaly or the start of a new trend. But the finding raises a flag for FAS as it works to increase gender diversity in a faculty where less than 19 percent of 478 tenured professors are women.

The report by Lisa L. Martin, the FAS senior adviser on diversity, called the drop a “troubling reversal.” The dramatic fall in women’s acceptances came even though the fraction of tenure-track offers to women rose slightly, to 39 percent, last academic year.

“It’s hard to know whether this is just a one-year blip or whatever,” Martin, the Dillon professor of international affairs, said in a phone interview. “All this shows is that of the offers made last year to men and women, women accepted at a much lower rate than the men.”

Harvard has sought in recent years to boost its ranks of women with tenure-track posts—assistant or associate professors who are eligible to be granted a tenured professorship—as a way to improve gender diversity in FAS.

The issue sparked national interest in early 2005, after then-University president Lawrence H. Summers suggested that a lack of “intrinsic aptitude” might account for the dearth of women in the sciences.

But according to the report, Harvard’s biggest problem may lie in recruiting faculty for the humanities. Martin found that only 34 percent of FAS tenure-track professors in the humanities are women—even though the percentage of students who gain PhDs in those disciplines now “substantially exceeds” 50 percent.

The report, which was completed in September and distributed at Tuesday’s Faculty meeting, also showed that the percentage of tenure offers made to women is still well below its 2000-2001 high.

Martin said the dip in offers to women—from 36 percent in 2000-2001, to about 12 percent three years later, and back up to 30 percent last year—was caused because “people sort of believed that the problem was just solved.”

“This is an issue that requires constant attention—it’s not a one-shot deal, unfortunately,” she said. “People weren’t paying enough attention, and now it’s obviously back on the agenda.”

The report partly attributed difficulties in retaining women faculty to a gap between the tradition of Harvard as a residential university and the reality that only 43 percent of FAS faculty now reside in Cambridge. Professors with family responsibilities are often forced to leave early from key meetings that last until 6 or 7 p.m.

To drive home the point, the report features comparative maps showing the spread of faculty residences outward from Cambridge since 1905. It calls on the Faculty “to reconsider the way that we do business on a day-to-day basis, and to recognize that practices that evolved when Harvard faculty were available on a round-the-clock basis to interact with colleagues and students are having a discriminatory and counterproductive effect today.”

Martin said in the interview that her main priorities for the year are to restructure searches for new faculty in a way that maximizes the applicant pool and to improve the mentoring of junior professors. Her report said that a program to form mentoring groups within academic divisions has been established, with funding for senior and junior faculty to meet for lunch once a semester.

In an e-mail response to questions, Interim Dean of the Faculty Jeremy R. Knowles did not address the drop in acceptances of tenure-track offers among women. He wrote: “I’m very pleased that Professor Martin has approached these issues with such thoughtful energy, and I strongly support the range of activities—from deepening our searches, to improving our maternity leave policies—that she has initiated.”

It is not clear how many women actually accepted tenure-track offers to join FAS. According to a University report released in June, the number of tenure-track faculty in FAS rose from 185 in 2004-2005 to 198 last academic year, and the number of women tenure-track professors saw a net increase from 65 to 72 over the same period.

—Staff writer Anton S. Troianovski can be reached at atroian@fas.harvard.edu.