SOUTH BEND, Indiana (Reuters) - President Barack Obama urged both sides in the abortion debate on Sunday to pursue a “fair-minded” discussion as he sought to quell a firestorm over his invitation to speak at Notre Dame, a premier U.S. Catholic university.

U.S. President Barack Obama addresses commencement ceremonies at the University of Notre Dame in South Bend, Indiana, May 17, 2009. REUTERS/John Gress

Notre Dame’s decision to confer an honorary degree on Obama and invite him to be the keynote speaker for the commencement sparked petitions and several days of protests. Some students vowed to boycott the commencement.

But the speech itself drew mostly cheers, applause and standing ovations.

Critics who said Obama’s support for abortion rights violated Catholic Church doctrine had sought to have the invitation rescinded but the university refused.

Interrupted at times by hecklers, Obama said he recognized the strong emotions stirred up by the abortion debate but he urged the two sides to try to find common ground, such as preventing unintended pregnancies.

“I do not suggest that the debate surrounding abortion can or should go away,” Obama said. “Each side will continue to make its case to the public with passion and conviction. But surely we can do so without reducing those with differing views to caricature.”

“Let us work together to reduce the number of women seeking abortions. Let’s reduce unintended pregnancies. Let’s make adoption more available. Let’s provide care and support for women who do carry their child to term,” Obama told the crowd of 12,000 at a huge athletic facility.

His appearance was mostly warmly welcomed by the crowd, which gave him several standing ovations.

SOME HECKLERS

But at a few points during the speech, he was interrupted by hecklers, including one who shouted, “Abortion is murder.” That heckler was booed by the audience.

Some graduates displayed a print of a cross symbol and two baby feet on their caps while others wore caps that said “Viva Obama.”

Outside the commencement, hundreds of protesters gathered and carried signs that said “Notre Dame supports violence” and “Thou shall not kill.”

As Obama spoke, protesters chanted outside the arena entrance: “One, two, three, four. Throw Obama out the door.”

At least 22 protesters were arrested after they walked past a piece of yellow police tape they had been told not to cross, according to police.

Norma McCorvey, the Jane Roe of the landmark Roe vs. Wade case that legalized abortion, was among the first protesters arrested at Notre Dame. A Catholic convert, McCorvey is now active in the anti-abortion.

Tony Ughetti, of Spring, Texas, said he watched as McCorvey asked the officers, “How do I get arrested?”

Ughetti said that in response to the Notre Dame decision to invite Obama, he got rid of books, T-shirts and other Notre Dame memorabilia in his home.

“We disposed of over 40 Notre Dame items from our house...I wanted to burn them but my wife took them to Goodwill (charity). Our house is now Notre Dame-free,” he said.

A smaller group of those outside were there in support of Obama’s visit. Carrying a sign reading “Welcome President Obama,” Bill Dillon, of South Bend, said he thought Obama was being treated unfairly.

“I don’t think they should call Obama a murderer,” said Dillon, a 1951 graduate in aeronautical engineering.

Catholics are the largest single denomination in the United States, making up nearly a quarter of the population. More than half of the adult population is Protestant but that is split among many denominations.

Many Catholics agreed with the university’s decision to invite Obama to speak at the commencement, according to a poll by the Pew Forum on Religion and Public Life.

Fifty percent of those in the poll agreed with the university’s invitation to Obama while 28 percent opposed it. The rest were undecided or had no opinion.