“How dare you honor him?” read a billboard on a road outside South Bend. A plane overhead pulled a banner with a picture of the feet of an aborted fetus.

Jon Buttaci, a graduating senior who boycotted the commencement ceremony in favor of a small vigil at the Grotto of Our Lady of Lourdes, said: “The Catholicism on this campus doesn’t match up with what the larger church is teaching. We’re standing up for prestige instead of standing up for the church.”

In his address, Mr. Obama did not engage on the merits of the debate on abortion; he instead made an appeal to each side of the issue. He said he supported a “sensible conscience clause” allowing health care providers to withhold abortion or other services that conflicted with religious beliefs. And he recalled agreeing with an anti-abortion voter who complained that his Senate campaign Web site in 2004 had demonized those who disagreed with Mr. Obama by calling them “right-wing ideologues.”

“Each side will continue to make its case to the public with passion and conviction,” he said. “But surely we can do so without reducing those with differing views to caricature.”

The modest protests here were amplified on national airwaves. “The problem here is that we’re trivializing abortion,” the Rev. Frank Pavone, national director of Priests for Life, said on “Fox News Sunday.” “But the people are speaking out. People are getting angry that 1.2 million children are being aborted every year.”

Michael Steele, chairman of the Republican National Committee and a Catholic, said Notre Dame should have allowed Mr. Obama to speak but not given him an honorary degree. “I think it’s inappropriate,” Mr. Steele said on “Meet the Press” on NBC. “And the president should speak, but the degree should not be conferred.”

The crowd inside the Joyce Center enthusiastically supported Mr. Obama, erupting into sustained cheers when he arrived. Some graduating students adorned their mortarboards with a yellow cross and baby feet, a symbol of the anti-abortion movement. But just as many had the president’s red-white-and-blue campaign logo on theirs, and the crowd sided with him against hecklers.