Amid protests by anti-abortion activists, U.S. President Barack Obama called for civility and spoke directly about the controversy surrounding his appearance Sunday at America's foremost Roman Catholic university.

Notre Dame graduate Kelly Kapshandy attended Sunay's commencement ceremonies. (Charles Rex Arbogast/Associated Press)

His speech to law school graduates began as hundreds of anti-abortion protesters gathered at the gates of Notre Dame University in South Bend, Ind., to protest the president's support of abortion rights and embryonic stem cell research.

Police said 37 people were arrested on trespassing charges and two others face both trespassing and resisting-arrest charges.

"I want to thank you for this honorary degree," Obama said early in his speech at commencement exercises. "I know it has not been without controversy."

He then spoke of the difficulties in attempting to "bridge the cultural divide" involving controversial issues.

"Those who speak out against stem cell research may be rooted in an admirable conviction about the sacredness of life, but so are the parents of a child with juvenile diabetes who are convinced that their son's or daughter's hardships might be relieved," he said.

As for the deeply divisive debate over abortion, Obama — who is pro-choice — said strong words can cause more division and that the two sides should extend the "presumption of good faith to others."

He said that during the presidential election campaign, he agreed with a doctor who objected to comparisons between those who are against abortion and "right-wing ideologues."

Obama said the doctor wrote him a letter urging the use of "fair-minded words," and soon the reference to the ideologues was removed from the Democratic candidate's website.

The president also urged those on either side of the debate to at least try to find areas of agreement.

"When we open up our hearts and our minds to those who may not think precisely like we do or believe precisely what we believe — that's when we discover at least the possibility of common ground," he said.

Urges support for women with unintended pregnancies

"That's when we begin to say, "Maybe we won't agree on abortion, but we can still agree that this heart-wrenching decision for any woman is not made casually. It has both moral and spiritual dimensions.

"So 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 children to term," Obama said.

Many associated with Notre Dame made their opposition to Obama's views known even before he arrived at the school to speak and receive the degree.

Some students demonstrated by putting a yellow cross with yellow baby's feet atop their mortarboards. Other students boycotted the graduation ceremony. South Bend Bishop John D'Arcy declined an invitation to attend.

More than 100 protesters showed up at the school Saturday to demonstrate against Notre Dame's invitation to Obama.

Nineteen of the protesters, who did not include any students, were arrested on trespassing charges, police said.

Among those arrested was Rev. Norman Weslin, founder of the Lambs of Christ abortion-protest group.

Bill Donohue, president of the Catholic League, said he has no problem with Obama speaking on campus during graduation ceremonies, but he's against the decision to give him an honorary degree.

In a letter to graduates last week, the president of Notre Dame, Rev. John Jenkins, said the university has a long custom of conferring honorary degrees to sitting U.S. presidents and its invitation does not change the school's commitment to "the sanctity of human life."

Obama is the ninth U.S. president to be awarded an honorary degree by the university and the sixth to be the commencement speaker.

With files from The Associated Press