Mr. Buttigieg also appealed directly to the young activists in the room.

“Mathematically, it is within the lifetime of anybody in college today that the situation in Israel, for Israelis and Palestinians, will either reach some kind of harmony, or catastrophe,” Mr. Buttigieg said. “You will live to see one of these two things happen.”

Former Housing Secretary Julián Castro received sustained applause from the audience when he said that he would re-establish a consulate in East Jerusalem that would serve as an embassy for Palestinians under a two-state solution.

“I am glad to see in this Democratic Party that the voices of folks who are concerned about the rights of Palestinians has emerged recently stronger, ” Mr. Castro said, speaking after Mr. Buttigieg. On the question of whether he would withhold aid from Israel, Mr. Castro said it “wouldn’t be my first move.”

Senator Amy Klobuchar of Minnesota also spoke at the conference, and declined to answer a question about military aid, saying only: “It’s not a good idea to negotiate these things right now.”

Senator Michael Bennet of Colorado also attended the conference and echoed his refrain that Democrats have moved too far to the left to attract swing voters, including on foreign policy.

The race’s two leading candidates, former Vice President Joe Biden and Senator Elizabeth Warren, did not attend the conference citing scheduling issues. But each of them recorded a video for the group, in which Ms. Warren repeatedly referred to the occupation, but Mr. Biden did not.