WASHINGTON (AFP) - Nearly one in four female undergraduates at leading US universities has been sexually assaulted, according to a new study.

The results supported those of previous studies, finding a similar preponderance of incidents of assault ranging from unwanted touching to rape.

The new study, released Monday by the Association of American Universities, found 23.1 per cent of female undergraduates were subjected to sexual contact by force or while incapacitated.

That percentage rose to 29.5 per cent among students identifying as "transgender, genderqueer, non-conforming, questioning, (or) something not listed on the survey."

In terms of penetration by force or while the victim was incapacitated, considered the most serious types of sexual assault, that "TGQN" category had the worst percentage, at 12.4 per cent, followed by undergraduate females at 10.8 per cent.

The study was conducted at 27 universities, and some of the highest rates of sexual assault were at Yale, University of Michigan and Harvard.

Several previous studies have found the rate of sexual assault on campus at approximately one in five women, but cross-college comparisons have been difficult due to varying definitions of assault and suspected self-reporting biases.

The AAU study lends new credibility to those past findings and gives a uniform picture of the assault crisis across many of the nation's campuses.

The perpetrators of those assaults are rarely charged by police or university authorities - only in five to 28 per cent of cases, according to some figures - but the White House has been leading a campaign for change, starting with convening a task force on college sexual assault last year.

California passed a "yes means yes" law, also last year, to define unambiguously what level of consent is needed for sexual activity to be consensual at the state's many colleges.