WASHINGTON — Attorney General Jeff Sessions dived into the debate over free speech on college campuses on Tuesday, inserting the Justice Department into a little-known lawsuit against a Georgia college and, in a speech that embraced First Amendment protections, comparing the tactics of one student group to the Ku Klux Klan.

Speaking at Georgetown University’s law school, Mr. Sessions condemned the designated free-speech zones that have popped up on campuses across the country and seized on the case of an evangelical Christian student who had been restricted from speaking about his religion. He also sided with provocative writers who have been controversial presences at the University of California, Berkeley, which has been at the center of the debate.

“A national recommitment to free speech on campus and to ensuring First Amendment rights is long overdue,” Mr. Sessions said, addressing an audience that included students wearing tape over their mouths in protest of the Trump administration. “Protesters are now routinely shutting down speeches and debates across the country in an effort to silence voices that insufficiently conform with their views.”

Mr. Sessions’s appearance drew dozens of demonstrators who dropped to one knee ahead of his speech, emulating the symbol of protest by N.F.L. players that President Trump has excoriated. The protesters — including Georgetown Law faculty members, more than four dozen of whom signed an open letter opposing Mr. Sessions’s policies — were themselves confined to protest zones by the university.