WASHINGTON — With a harsh denunciation both of a MoveOn.org ad mocking General David Petraeus and the Democratic leaders who stood by it, President Bush is wading into the campaign to succeed him and setting off another flurry of political maneuvering over the Iraq war.

“I thought the ad was disgusting,” Mr. Bush said yesterday morning at a White House press conference, referring to the New York Times display in which MoveOn.org referred to the commander of American forces in Iraq as “General Betray Us.”

“I was disappointed that not more leaders in the Democrat Party spoke out strongly against that kind of ad,” the president said when asked about Democratic candidates who did not rebuke the MoveOn ad, accusing them of being more fearful of alienating a left-wing anti-war group than of alienating America’s military.

“That leads me to come to this conclusion: that most Democrats are afraid of irritating a left-wing group like MoveOn.org — or more afraid of irritating them than they are of irritating the United States military.”

Mr. Bush added: “That was a sorry deal. It’s one thing to attack me; it’s another thing to attack somebody like General Petraeus.”

Within an hour of the president’s comments, the Senate voted overwhelmingly to condemn “personal attacks” on General Petraeus, but without the backing of the two leading Democratic presidential candidates, Senators Clinton and Obama. Mrs. Clinton voted against the symbolic measure, while Mr. Obama refused to cast a vote.

The resolution, which said General Petraeus “deserves the full support of the Senate” and that lawmakers “strongly condemn personal attacks on the honor and integrity of General Petraeus and all members of the United States Armed Forces,” passed by a 72–25 vote. It was introduced by Senator Cornyn, a Republican of Texas.

Mrs. Clinton and Mr. Obama have largely dodged direct questions about the ad while emphasizing that their criticisms of Iraq war policy are aimed at Mr. Bush, not General Petraeus.

The Illinois senator issued a statement saying, “the focus of the United States Senate should be on ending this war, not on criticizing newspaper advertisements.”

“This amendment was a stunt designed only to score cheap political points,” Mr. Obama added. “It’s precisely this kind of political game-playing that makes most Americans cynical about Washington’s ability to solve America’s problems. By not casting a vote, I registered my protest against this empty politics.”

A spokesman for Mrs. Clinton offered no explanation for her vote, which drew an immediate attack from a Republican candidate, Mitt Romney. “The idea that she would be a credible commander in chief of our armed forces requires the willing suspension of disbelief,” Mr. Romney said in a statement.

While no leading Democratic candidate has outright defended the MoveOn.org ad, the refusal to repudiate the group reflects its perceived influence with the party’s base. “There’s more to lose than there is to gain in denouncing MoveOn.org,” a Democratic consultant who is the interim dean of Boston University’s College of Communication, Tobe Berkovitz, said.

Of the two other Democratic candidates in the Senate, Senator Dodd of Connecticut voted against the resolution while Senator Biden of Delaware did not vote.

Senate Democrats also fell far short yesterday of forcing the president to withdraw troops from Iraq, mustering just 28 votes for a bill that would have cut off funding for the war by June. It was the second day in a row that Democratic leaders failed in efforts to mandate a different war strategy.

President Bush’s criticism of the Democratic candidates yesterday were not his only remarks on the 2008 White House race, as he strayed briefly from what had been a self-imposed prohibition on commenting on the campaign — or as he once put it, becoming the “pundit in chief.”

Mr. Bush offered advice to Republican hopefuls and declared confidently that he would be a “strong asset” rather than a liability, despite his low approval ratings.

“Candidates who go out and say that the United States is vulnerable to attack and we’re going to make sure our professionals have the tools necessary to protect us are going to do well,” he said. “Candidates who go out and say that helping these Iraqis realize the benefits of democracy are going to do well.”

He added that candidates should state “clear principles” on foreign policy and that “candidates who say we’re not going to raise your taxes are going to do well.”

Following decisions by the leading GOP candidates to decline invitations to speak at forums before black and Hispanic audiences, Mr. Bush also pushed them to reach out more to minority communities.

While Republicans like Mr. Romney and Mayor Giuliani are careful not to attack the president directly, they have not embraced his legacy on many issues and often emphasize themes of “change” on the campaign trail. “My guess is this has irritated Bush considerably, and he may be firing back,” the director of the University of Virginia’s Center for Politics, Larry Sabato, said.