Mary Ann Glendon, a Harvard Law School professor and prominent Roman Catholic conservative who served as ambassador to the Vatican under President George W. Bush, today declined a prestigious medal from the University of Notre Dame in protest of its decision to invite President Obama speak at its commencement.

In a letter to Notre Dame’s president, the Rev. John I. Jenkins, that was reprinted today on a Boston Globe blog, Ms. Glendon said she “could not help but be dismayed” when she learned that Notre Dame planned to award an honorary degree to Mr. Obama during the same commencement ceremony in which she was to be awarded the university’s Laetare Medal for her service to the Roman Catholic Church and the nation as a whole.

Ms. Glendon’s letter characterized the university’s decision to award an honorary degree to President Obama as disregarding a 2004 request by American bishops that Catholic institutions “not honor those who act in defiance of our fundamental moral principles.” She expressed concern that Notre Dame’s decision could have the “unfortunate ripple effect” of inspiring other Catholic colleges to similarly choose to disregard the bishops’ guidelines.

Ms. Glendon’s letter also took issue with talking points that Notre Dame had issued in response to criticism of its invitation to President Obama. In the talking points, she said, the university implied her acceptance speech for her award “would somehow balance the event.”

Her letter said a commencement “is not the right place, nor is a brief acceptance speech the right vehicle, for engagement with the very serious problems raised by Notre Dame’s decision — in disregard of the settled position of the U.S. bishops — to honor a prominent and uncompromising opponent of the church’s position on issues involving fundamental principles of justice.”

Father Jenkins responded to the letter with a written statement saying he was “disappointed” with her decision. “It is our intention to award the Laetare Medal to another deserving recipient, and we will make that announcement as soon as possible,” the statement said.

Ms. Glendon served President Bush both as Vatican ambassador and as a member of his Council on Bioethics, and she headed a panel that Mitt Romney, a Republican, picked to advise him on judicial matters during his run for president last year. She was one of 60 prominent American scholars who in 2002 signed a letter defending the nation’s “war on terror” as “not only morally permitted, but morally necessary.”

Pope John Paul II appointed her to the Pontifical Academy of Social Sciences, and she served as the Vatican’s representative at the United Nations’ 1995 Beijing Conference on Women, in which she presented the church’s view that condoms should not be used for family planning or in HIV-prevention programs. —Peter Schmidt