In four years of college, more than one-fourth of undergraduate women at a large group of leading universities said they had been sexually assaulted by force or when they were incapacitated, according to one of the largest studies of its kind, released Monday.

Responding to a survey commissioned by the Association of American Universities, 27.2 percent of female college seniors reported that, since entering college, they had experienced some kind of unwanted sexual contact — anything from touching to rape — carried out by incapacitation, usually due to alcohol or drugs, or by force. Nearly half of those, 13.5 percent, had experienced penetration, attempted penetration or oral sex.

The survey bolstered findings from previous studies but stands out for its sheer size — 150,000 students at 27 colleges and universities took part last spring — and for the prominence of the institutions involved, which include many of the nation’s elite campuses, including all of the Ivy League except Princeton.

Last year, President Obama convened the first White House task force on college sexual assault, part of a growing demand for colleges to acknowledge, measure and address the problem. That task force, like members of Congress and victim advocates, called on colleges to conduct rigorous “campus climate” surveys, including detailed information on the frequency of assault and harassment.