WASHINGTON -- Sen. Rick Santorum is demanding a formal apology from Senate Minority Leader Harry Reid for what he views as an ethnic slur.

Earlier this week on PBS's "The News Hour with Jim Lehrer," Mr. Reid, D-Nev., said "having Senator Santorum talk about [lobbying] reform is like having John Gotti talk about doing something about organized crime."

Mr. Santorum, R-Pa., who is Italian, also took offense to a Web advertisement put out by the Democratic Senatorial Campaign Committee describing Mr. Santorum as "the Godfather" of the K Street project -- an effort by Republicans to get more candidates from their party hired at the top lobbying firms that are generally located along Washington's K Street.

This week, Mr. Santorum denied any involvement in the K Street Project.

"While you may think my leadership in the Senate's effort to reform the country's existing lobbying laws is fair game for attack, my ancestry is not," Mr. Santorum said in his letter to Mr. Reid. "I join leaders in the Italian-American community in expressing outrage over the repeated slurs aimed at millions of us."

Jim Manley, Mr. Reid's spokesman, said he thought Mr. Santorum was being "thin-skinned" about his ties to lobbyists.

"Who knew he was Italian?" Mr. Manley said.