Marquette University on Thursday abruptly rescinded an offer to a sociologist to serve as dean of one of its colleges, angering some students and faculty members who said the university did so after learning she was a lesbian who wrote about sexuality.

Marquette, a Roman Catholic university run by Jesuits in Milwaukee, said the professor lacked “the ability to represent the Marquette mission and identity.”

The professor, Jodi O’Brien, who teaches sociology at Seattle University, is openly gay and writes frequently about sexuality in academic journals.

Nancy E. Snow, a professor of philosophy at Marquette who had supported Dr. O’Brien’s candidacy for dean of the College of Arts and Sciences, said of the decision, “This is discrimination based on sexual orientation, and is a complete betrayal of our commitment to human dignity and diversity.”