Senator Obama’s opposition to Columbia University’s ban on the Reserve Officers’ Training Corps is reigniting a campus debate, with several student leaders pushing for a student-wide referendum about whether the military program should be allowed back to Morningside Heights.

A vote to gauge the opinion of the entire student body on a repeal of the 40-year-old ban could come as early as this week.

A Columbia junior who is a marine officer candidate, Austin Byrd, said that the campus is abuzz about Mr. Obama’s opposition, which he discussed at a forum on community service held at the university last week. He said he was surprised by the Democratic presidential candidate’s “unabashed support” for allowing the program back on campus.

Other students said that the crowd of 7,500 that had gathered to watch the speech outside was similarly shocked.

A junior at Columbia, Jordan Hirsch, said that Mr. McCain was booed by students when he voiced his opposition to the ban, but that when Mr. Obama expressed a similar sentiment, the crowd had a different response.

“Almost everyone’s expecting him to say no, because he’s on our side, right? So then you heard him say ‘yes’ and everyone’s mouths opened in stunned silence. It was absolutely priceless,” Mr. Hirsch said.

The upcoming referendum would be the second such vote that has taken place since 2003. In April of that year, 65% of students voted in support of ROTC’s return, but when the issue came before the university senate in 2005, repealing the ban was overwhelmingly opposed.

The senate includes a handful of student representatives among a faculty majority. Columbia’s president, Lee Bollinger, voted in favor of upholding the ban.

ROTC began in 1916 at Columbia and was responsible for training about 100,000 American servicemen to fight in World War II. In the wake of the Vietnam War and sometimes violent antiwar student protests, in 1969 university trustees voted to kick ROTC off campus.

Those in favor of the ban today argue that the military’s “Don’t Ask Don’t Tell” policy toward gays violates the university’s antidiscrimination policy.

Columbia students are allowed to be members of ROTC, but must travel to Fordham University or Manhattan College in the Bronx for training and receive no Columbia class credit.

“I don’t think it should be on campus. I think Don’t Ask Don’t Tell is a really discriminatory policy and Columbia has a very strict nondiscriminatory statement,” the president of Columbia’s College Democrats, Christopher Daniels, said.

The executive director of the College Republicans, Lauren Salz, said she wants to see ROTC on campus. “I was glad that Obama said it, and maybe it will make people think twice about their opposition to ROTC on campus,” Ms. Salz said.

Many student leaders insist that the decision to have a student-wide vote on the matter was in the works long before Mr. Obama and Mr. McCain’s visit. Rajat Roy, a junior and a university senator, said he began working on the issue last spring when a would-be marine asked him why ROTC wasn’t on campus. “The issue of ROTC is not about the candidates, it’s about the students,” he said.