Attorney General Mukasey said yesterday he will refuse to publicly say whether the interrogation tactic known as waterboarding is illegal, digging in against critics who want the Bush administration to define it as torture. In a letter to the Senate Judiciary Committee chairman, Patrick Leahy, Judge Mukasey said he has finished a review of Justice Department memos about the CIA’s current methods of interrogating terror suspects and finds them to be lawful. He said waterboarding currently is not used by the spy agency. Since waterboarding is not part of what Judge Mukasey described as a “limited set of methods” used by interrogators now, the attorney general said he would not rule on whether it is illegal. “I understand that you and some other members of the [Judiciary] Committee may feel that I should go further in my review, and answer questions concerning the legality of waterboarding under current law,” Judge Mukasey wrote in his three-page letter to Mr. Leahy. “I understand the strong interest in this question, but I do not think it would be responsible for me, as attorney general, to provide an answer.”