Women are far more likely than men to be kicked out of the military under the "don't ask, don't tell" policy against gays in uniform, according to government figures released Thursday that critics said reflect deep-seated sexism in the armed forces.

Women accounted for 15 percent of all active-duty and reserve members of the military but more than one-third of the 619 people discharged last year because of their sexual orientation.

The disparity was particularly striking in the Air Force, where women represented 20 percent of all personnel but 61 percent of those expelled. That is a significant jump from the previous year and marks the first time women in any branch of the military constituted a majority of those dismissed under "don't ask, don't tell," researchers said.

Nathaniel Frank, a researcher at the Palm Center, a University of California, Santa Barbara, center specializing in gays and the military, said one partial explanation is that homosexuality is more common among women in the service than among their male comrades.

But Frank and some women who served in the military said the gap could also be a result of "lesbian-baiting" rumors and investigations that arise when women rebuff sexual overtures from male colleagues or do not meet traditional notions of feminine beauty.

"Often times the lesbians under my command were under scrutiny by the same men who were also sexually harassing straight women, so it was this kind of sexist undercurrent of 'You don't belong here,'" said Anuradha Bhagwati, a former Marine who founded the Service Women's Action Network, an advocacy group.

Pentagon spokeswoman Cynthia Smith said officials would not speculate on why women accounted for a disproportionate share of those dismissed for being gay, adding that even inquiring about it might run afoul of "don't ask, don't tell."

"If we did investigate it, we would have to ask questions, and we aren't supposed to ask any questions," Smith said.

Under the 1993 policy, gay men and lesbians in the military cannot be investigated or punished as long as they keep their sexual orientation to themselves. The policy has led to the discharge of about 13,000 service members.

The latest statistics were obtained from the Pentagon by the Palm Center and released as activists step up pressure on President Barack Obama to sign an executive order repealing the gay ban in the military. The president is scheduled to deliver the keynote address Saturday at a fundraising dinner for the nation's largest gay rights group. A White House spokesman said the president "is intent on making progress" on the issue.

In 2007, 49 percent of Air Force personnel discharged for being gay were women, up from 36 percent in 2006.

In the Army, women accounted for 14 percent of personnel and 36 percent of the "don't ask, don't tell" discharges in 2008; in the Navy, it was 14 percent of the personnel and 23 percent of the discharges, and in the Marines, 6 percent and 18 percent.

"It's very clear the military comes down harder on women than on men, but the question of whether they come down harder on lesbians than on gay men is harder to answer," said Palm Center director Aaron Belkin. "We don't know whether the statistics reflect lesbian-baiting or just a higher rate of lesbians in the military."

Frank said the increases are all the more surprising because the "don't ask, don't tell" policy was largely driven by the argument that "straight men won't tolerate serving alongside known gays."

Julianne Sohn, the lone female Marine officer discharged under the policy last year, was a lieutenant who had served a seven-month tour in Iraq as a reservist when she received a telephone call at home from a lieutenant colonel informing her she was under investigation for being a lesbian.

The call was not a surprise. Some of her fellow Marines, who knew about her sexual orientation, had given her a heads-up a few months before.

Sohn had been speaking publicly about her experience as a gay officer as part of an organized effort to spotlight the costs of "don't ask, don't tell." She said she could not respond honestly when colleagues wanted to know why she did not have a boyfriend, and said she asked her brothers to contact her girlfriend if she were killed in Iraq because she did not want to list a woman as her next of kin.

Sohn, 33, who now works as a police officer in Los Angeles, said hearing the investigating officer read her the military's equivalent of a criminal suspect's Miranda warning over the phone was a fresh insult.

"The way I look at is, all I've done is tell my story," said Sohn, who did not fight the inquiry and was honorably discharged. "I wanted to serve, and I did serve."