PITTSBURGH — Duquesne University has told its law school that it cannot invite politicians, including U.S. Sen. Barack Obama and U.S. Rep. John Murtha, to speak at graduation.

A policy adopted in June recommends the school generally avoid politicians as commencement speakers, said President Charles Dougherty. Such high-profile politicians would be "sure to offend large numbers in the audience," he said.

"Even if such a speaker steers clear of political content, it makes a political statement that we provided them an occasion and a platform and one in which there is no possibility for dialogue or the expression of alternative points of view," he said.

Law school Dean Donald Guter had sought approval to approach Obama, Murtha and others.

Dougherty said the policy does not mean politicians are not welcome on the Catholic campus. Also, exceptions could be made, such as for presidents and governors, a spokeswoman said Thursday.

Sheldon Steinbach, a higher education law specialist and retired general counsel at the American Council on Education, said he never heard of such a restriction.

Distinguishing between politicians and executive officeholders "is a distinction without a difference," he said. "Precluding political leaders of any stripe from consideration seems to be narrow-minded."