WASHINGTON — Senator Clinton will oppose the nomination of Judge Michael Mukasey for attorney general, joining her rivals for the Democratic presidential nod but setting up a possible clash with Senator Schumer, who recommended Judge Mukasey to lead the Justice Department.

Mrs. Clinton issued a statement through her Senate office this afternoon, a move that came less than a day after her top competitors, Senator Obama and John Edwards, announced their opposition to Judge Mukasey. She cited the retired federal jurist’s responses to questions about interrogation techniques and executive power, in which he has refused to say whether he believes waterboarding is a form of torture. He has also suggested, to the dismay of several senators, that the president has the authority to disobey a constitutional federal statute in an effort to defend the nation.

“Judge Mukasey has been given ample opportunity — both at his confirmation hearings and in his subsequent submission to the Judiciary Committee — to clarify his answers and categorically oppose the unacceptable interrogation techniques employed by this administration,” Mrs. Clinton said. “His failure to do so leaves me no choice but to oppose his nomination.”

Members of the Judiciary Committee, including the chairman, Senator Leahy of Vermont, and Mr. Schumer, are still awaiting responses from Judge Mukasey to a series of letters and written questions asking him to clarify his views on torture and presidential power. Some lawmakers have said that unless he explicitly denounces waterboarding — a technique that involves simulated drowning — they will not support him.

The White House said today that those responses could arrive by the end of the day. But Mrs. Clinton, like Mr. Obama, said she decided that Judge Mukasey shouldn’t have needed a second chance to make his views clear. She may have decided to put her statement out immediately because of the likelihood that she will be asked directly about Judge Mukasey when the Democratic candidates meet tonight for a debate in Philadelphia.

A spokesman had hinted at her likely opposition yesterday, telling The New York Sun that Mrs. Clinton had been “deeply troubled” by Mr. Mukasey’s answers on torture and executive authority.

Her opposition likely puts her at odds with Mr. Schumer, who warmly introduced Judge Mukasey at his confirmation hearing and who initially predicted he would win Senate approval by “a large majority.” Yet with doubts arising about the certainty of Judge Mukasey’s confirmation, Mr. Schumer has declined to say categorically whether he will vote for him. The senator’s spokesman did not return calls yesterday.