WASHINGTON  In nearly four months in office, President Obama has pursued a careful two-pronged strategy on abortion, enacting policies that secure a woman’s right to the procedure while vowing to move beyond the culture wars that have divided the nation on the issue for more than three decades.

Now, Mr. Obama is suddenly in the thick of the battle he had hoped to transcend, and his delicate balancing act is being put to the test.

The confluence of two events  his commencement speech on Sunday at the University of Notre Dame, in Indiana, and his forthcoming choice of a candidate to replace Justice David H. Souter, who is retiring from the Supreme Court  threaten to upend Mr. Obama’s effort to “tamp down some of the anger” over abortion, as he said in a news conference last month, and to distract from his other domestic priorities, like health care.

The invitation from Notre Dame, a Roman Catholic institution, has riled opponents of abortion, who object to giving such a platform to a supporter of abortion rights. The local bishop has vowed to boycott the ceremony. Some graduating seniors are planning to protest it. Conservatives, frustrated by what they regard as Mr. Obama’s skillful efforts to paint himself as a moderate, are all over the airwaves denouncing him as “the most radical, pro-abortion of any American president,” as Newt Gingrich, a former House speaker, said on Fox News.