SOUTH BEND, Ind. — President Barack Obama strode head-on Sunday into the stormy abortion debate and told graduates at America’s leading Roman Catholic university that both sides must stop demonizing one another.

Obama acknowledged that “no matter how much we want to fudge it … the fact is that at some level, the views of the two camps are irreconcilable.” But he still implored the University of Notre Dame’s graduating class and all in the U.S. to stop “reducing those with differing views to caricature. Open hearts. Open minds. Fair-minded words. It’s a way of life that always has been the Notre Dame tradition.”

One of the noisiest controversies of his young presidency flared after Obama, who supports abortion rights but says the procedure should be rare, was invited to speak at the school and receive an honorary degree. “I do not suggest that the debate surrounding abortion can or should go away,” the president said.

The Rev. John Jenkins, Notre Dame’s president, introduced Obama and praised the president for not being “someone who stops talking to those who disagree with him.” Jenkins said too little attention has been paid to Obama’s decision to speak at an institution that opposes his abortion policy.

Ahead of Obama’s address, at least 27 people were arrested on trespassing charges. They included Norma McCorvey, the plaintiff identified as “Roe” in the Roe v. Wade Supreme Court decision that legalized abortion. She now opposes abortion and joined more than 300 anti-abortion demonstrators at the school’s front gate.

More than half held signs, some declaring “Shame on Notre Dame” and “Stop Abortion Now” to express their anger over Notre Dame’s invitation to Obama.

Obama entered the arena to thunderous applause and a standing ovation from many in the crowd of 12,000. But as the president began his commencement address, at least three protesters interrupted it. One yelled, “Stop killing our children.”

The graduates responded by chanting “Yes we can,” the slogan that became synonymous with Obama’s presidential campaign. Obama seem unfazed, saying Americans must be able to deal with things that make them “uncomfortable.”

The president ceded no ground. But he said those on each side of the debate “can still agree that this is a heart-wrenching decision for any woman to make, with both moral and spiritual dimensions.

“So let’s work together to reduce the number of women seeking abortions by reducing unintended pregnancies, and making adoption more available, and providing care and support for women who do carry their child to term.”

He said he favored “a sensible conscience clause” that would give anti-abortion health care providers the right to refuse to perform the procedure.

Before taking on the abortion issue, Obama told graduates they were part of a “generation that must find a path back to prosperity and decide how we respond to a global economy that left millions behind even before this crisis hit an economy where greed and short-term thinking were too often rewarded at the expense of fairness, and diligence, and an honest day’s work.”

Obama’s appearance appeared additionally complicated by fresh polls that show Americans’ attitudes on the issue have shifted toward the anti-abortion position.

A Gallup survey released Friday found that 51 percent of those questioned call themselves “pro-life” on the issue of abortion and 42 percent “pro-choice.” This is the first time a majority of U.S. adults have identified themselves as “pro-life” since Gallup began asking this question in 1995.

Just a year ago, Gallup found that 50 percent termed themselves “pro-choice” while 44 percent described their beliefs as “pro-life.”

A Pew Research Center survey found public opinion about abortion more closely divided than it has been in several years.

Pew said its latest polling found that 28 percent said abortion should be legal in most cases while 18 percent said all cases. Forty-four percent of those surveyed were opposed to abortion in most or all cases.

Gallup said shifting opinions lay almost entirely with Republicans or independents who lean Republican, with opposition among those groups rising over the past year from 60 percent to 70 percent.

The abortion issue also is front and center as Obama considers potential nominees to fill the vacancy left by the retirement this summer of Justice David Souter. Abortion opponents are determined to see Roe v. Wade overturned, but only four court justices out of nine have backed that position. Souter has opposed arguments for overturning the ruling.

The Catholic Church and many other Christian denominations hold that abortion and the use of embryos for stem cell research amount to the destruction of human life, are morally wrong and should be banned by law.

The contrary argument holds that women have the right to terminate a pregnancy and that unused embryos created outside the womb for couples who cannot otherwise conceive should be available for stem cell research. Such research holds the promise of finding treatments for debilitating ailments.

Within weeks of taking office in January, Obama eased an executive order by President George W. Bush that limited research to a small number of stem-cell strains.

On the Notre Dame campus, members of an abortion rights group also protested while a plane pulling an anti-abortion banner circled above. Tara Makowski of Seattle, who received a master’s degree Saturday from the school, said she was dismayed by the way Notre Dame was being characterized.

“Seeing us being portrayed nationally as radical conservative has been really tough,” she said. “People need to realize that the majority of students and faculty” favored Obama’s visit.

But Bishop John D’Arcy, whose diocese includes Notre Dame, skipped commencement. He attended an open-air Mass and rally. He said he wanted to support the students protesting Obama’s speech.

“All of you are heroes, and I’m proud to stand with you,” he said.

Obama was the ninth president to receive an honorary degree from Notre Dame and sixth sitting president to address graduates. Other commencement speakers have included Dwight Eisenhower, Jimmy Carter, Ronald Reagan, George H.W. Bush and George W. Bush.

Back in Washington, Vice President Joe Biden attended Mass with his family at Holy Trinity Church, where a granddaughter received her first Communion.