NEW HAVEN, Conn. (AP) – More than 100 Yale University graduate students marched to the president’s office Thursday to protest what they said is inequitable treatment of women at the Ivy League university.

The students, many of whom are trying to form a union, criticized President Richard Levin for not joining the presidents of Stanford, Princeton and the Massachusetts Institute of Technology in denouncing comments made last month by Harvard President Larry Summers.

Summers said biological differences may help explain why more men than women excel in science. He has since apologized several times.

“Summers’ comments revealed a systemic problem,” said Melissa Mason, co-chairwoman of the Graduate Employees and Student Organization. “Levin, as head of an Ivy League university, has a responsibility to respond.”

Levin was not in his office Thursday. The university said he was in Washington. Students left a letter at his office and spoke to other administrators. Reporters were not allowed inside.

“President Levin has devoted a great deal of his presidency to ensure that we increase the number of ladder and tenured female faculty at Yale,” spokeswoman Helaine Klasky said.

Of the 881 tenured Yale faculty members, 168 – or 19 percent – are women. That percentage has nearly doubled in the past decade, a statistic that university officials say reflects their commitment to improvement.

All of Yale’s regular math faculty members are men and there is only one black woman with tenure at the university – Hazel V. Carby, a professor of African American studies. She said there are still hurdles for women to clear if they are to advance.

“When I came to Yale, there were actually two African American women with tenure, so we’ve gone backward,” said Carby, who was not involved in the protest.

Meg Urry, a tenured physics professor, wrote an op-ed piece for The Washington Post this month about the difficulties women face in the scientific fields. She concluded that women have slowly been making progress, however, and that Yale treats her wonderfully.

University officials said they have taken several steps to make it easier for women to advance, including expanding the school’s family leave policy, which allows professors to take time off after child birth without jeopardizing the tenure process. The school is also developing a plan to address child care needs.

“These new policies are part of a larger effort now underway to find ways to help members of the Yale community balance the competing needs of their working and families lives,” Susan Hockfield wrote to the faculty in October, when she was the school’s provost.

Pro-union graduate students made it clear that they saw Thursday’s rally as part of their union drive. The group is still regrouping from a 2003 vote in which graduate students rejected the union.

The diversity issue has been a complaint among the pro-union students. They have also called for expanded health care, including free health insurance for the dependent families of graduate students.

Yale graduate students attend classes for free, receive free health care and are paid yearly stipends of about $20,000 to teach or research, the university said.