WASHINGTON — Support for the nomination of Judge Michael Mukasey as attorney general is plummeting among Democratic presidential hopefuls, with Senator Obama coming out against the retired federal jurist and Senator Clinton sending her strongest signal yet that she also may oppose his confirmation.

Mr. Obama, the Illinois senator running second to Mrs. Clinton in national polls, last night joined three other Democratic candidates in opposing Judge Mukasey, who has met increased resistance from senators in both parties over his statements about presidential power and his refusal to repudiate waterboarding as a form of torture.

“Judge Mukasey has failed to send a clear signal that he understands the legal and moral issues that are at stake for our country, and so I cannot support him,” Mr. Obama said in a statement sent to The New York Sun by his campaign last night.

His statement came hours after Senator Dodd of Connecticut became the first presidential candidate and just the second senator to publicly announce his opposition to President Bush’s choice to lead the Justice Department. Also yesterday, aides to John Edwards and Governor Richardson told the Sun that they too opposed Judge Mukasey, increasing the pressure on Mrs. Clinton to follow suit.

While Judge Mukasey said repeatedly and unequivocally in confirmation hearings earlier this month that torture was illegal, he has not said whether he believes torture includes waterboarding, an interrogation method that simulates drowning. Members of the Senate Judiciary Committee have pressed Judge Mukasey in letters and written questions on this issue, and several have suggested that their vote will hinge on his response.

Mr. Obama said even a clarification from Judge Mukasey would be insufficient. “No nominee for attorney general should need a second chance to oppose torture and the unnecessary violation of civil liberties,” he said.

Mrs. Clinton has not said how she will vote on the nomination, but she appears to be moving closer to the ‘no’ column. “Senator Clinton is deeply troubled by Judge Mukasey’s unwillingness to clearly state his views on torture and unchecked executive power,” a spokesman for her Senate office, Philippe Reines, told the Sun in an e-mail yesterday.

Mr. Reines refused to say whether that meant that Mrs. Clinton intended to oppose Judge Mukasey or even whether she has made a final decision, but the statement was stronger than what the senator has said previously. In an interview with the Guardian newspaper last week, she was more vague, saying only that Judge Mukasey’s responses “in a number of areas raised issues for me” and that his answer on interrogation methods was “a concern.”

She could be pressed for a more concrete answer when the Democratic candidates meet tonight for a debate in Philadelphia.

The nomination is a potentially prickly issue for Mrs. Clinton that could pit presidential politics against home state loyalties. Judge Mukasey is a native New Yorker who won a recommendation from Mrs. Clinton’s colleague and ally, Senator Schumer.

Mr. Schumer, who sits on the Judiciary Committee and had led the calls for Mr. Gonzales to resign, gave Judge Mukasey a warm introduction at his hearing and had said he expected him to be confirmed by a “large majority.”

But even he has not said definitively whether he will vote for confirmation, and he could very well be the pivotal voice in determining whether Judge Mukasey wins approval from the Democratic-controlled Senate. Last week, he was one of 10 committee members to send the judge a series of detailed questions seeking clarification on a range of issues, including the use of executive privilege and executive authority.

The committee chairman, Senator Leahy of Vermont, has said he will not schedule a vote on Judge Mukasey until he receives responses to the various questions and separate letters sent to the nominee. If they arrive by today, a vote could occur as early as Thursday. The White House has chastised the committee for dragging their feet on the nomination, but a spokeswoman, Dana Perino, said lawmakers would see responses from Judge Mukasey this week.

Both Democrats and Republicans have taken issue with Judge Mukasey’s statement at his hearing that he did not know what was involved in waterboarding, a technique that has drawn widespread attention in recent months. “Anyone who says they don’t know if waterboarding is torture or not has no experience in the conduct of warfare and national security,” a Republican presidential candidate, Senator McCain of Arizona, said on ABC’s “This Week” on Sunday. His sentiment was echoed in large measure by Senator Graham of South Carolina and Senator Specter of Pennsylvania, the ranking Republican on the Judiciary Committee.

The White House and Judge Mukasey have said he cannot speak to specific interrogation methods because they are classified and that he won’t have the requisite clearance until he takes over.

Mr. Dodd raised a separate issue in announcing his opposition yesterday. He cited Judge Mukasey’s response when asked if the president could disobey a constitutional federal statute. The judge said it would depend whether the action in question “nonetheless lies within the authority of the president to defend the country.” Mr. Dodd said it was an “extraordinary statement” that suggested the president was above the law. It demonstrated, he said, “a failure to fundamentally understand that we are a nation of laws and not man.”