“The petition’s primary aim is very much akin to pressuring someone that you love very much into going into rehab,” Mr. Blatty wrote me in an e-mail. He has deep roots at Georgetown. He attended on full scholarship, set his blockbuster horror story on campus and named his new watchdog group, the Father King Society to Make Georgetown Honest, Catholic and Better, after the late Thomas M. King, a beloved theology professor.

Other groups, too, have made it their business to monitor Catholic colleges. The Fellowship of Catholic Scholars was critical of Notre Dame for inviting President Obama, who supports abortion rights, to give a commencement address. The Cardinal Newman Society, founded in 1993 by a Fordham University alumnus, has attacked Boston College for turning a blind eye when students distribute condoms and DePaul University for allowing a production of “The Vagina Monologues.” The Cardinal Newman Society has also taken aim at Georgetown for Genderfunk. This year, a male student went as a high-heeled Mary and danced to Madonna’s “Like a Virgin” while Jesus (a woman) looked on.

Several pages of the Georgetown memorandum are dedicated to Mr. Tisa, his “irrepressible and well-trained gay agenda” and his attempts at “cleverly redefining what Catholic means.”

Cardinal Wuerl declined to comment, but Rachel Pugh, a Georgetown spokeswoman, pointed to the university’s two required theology classes and up to seven Sunday Masses at the main chapel as evidence that it is deeply connected to its Catholic identity. The university also organizes church retreats and regular Eucharistic adoration ceremonies. Dozens of priests live on campus and serve as spiritual mentors.

“Our Catholic and Jesuit identity on campus has never been stronger,” Ms. Pugh said. “Academically, we remain committed to the Catholic intellectual tradition.”

Many students have an entirely secular experience at Georgetown. Sitting on a knoll overlooking the Potomac River, the university is a magnet for political junkies wanting access to the Capitol. But the obsession with politics is only part of the Georgetown story. Half of undergraduates identify as Catholic. The university’s religious underpinnings are embedded in its philosophy, and so, too, is what some students refer to as “the God conversation,” a dialogue about Jesuit values that regularly arises inside and outside of class.

The Jesuit educational model created by St. Ignatius of Loyola has a distinctly humanist bent. Todd A. Olson, Georgetown’s dean of students, says he is confident that providing gay students support, freedom of expression and a place to celebrate who they are does not conflict with the university’s Jesuit heritage. He cites cura personalis, the Jesuit tenet that loosely translates into care of the whole person, saying that Georgetown has an obligation to concern itself with the well-being of all its students.