America is at a crossroads in Iraq and must decide soon whether to withdraw or make a commitment for victory, Senator McCain of Arizona said.

“I’m not prepared to go to an American family and tell them, ‘Well, you know, we’ll — you just stay there for a while, and we’ll delay this withdrawal and defeat for a year or two,'” Mr. McCain said during an interview yesterday on NBC’s “Meet the Press.” “I’m prepared to tell them that if we have the will to win, we will do what’s necessary to win. But I’m not interested in seeing a scene. … on the roof of the American embassy in Saigon multiplied a thousand fold.”

Mr. McCain, who is considering running for the White House in 2008, has proposed increasing the number of American troops in Iraq by about 20,000. He did not repeat that figure yesterday but made clear he still favors keeping a robust American military presence there in an attempt to shore up the Iraqi government.

“We’re in a critical and crucial time. We’re either going to lose this thing or win this thing within the next several months,” the senator said. “I believe the consequences of failure are chaos in the region, which will spread.”

Other national political figures, however, are losing confidence in the fledgling Iraqi government. The chairman of the Democratic National Committee, Howard Dean, suggested yesterday that America scale back its goals simply to maintaining security in Iraq.

“It is not our job to prop up an incompetent regime, and this regime in Iraq looks more and more incompetent as time goes along. So it is our job to keep order. We can do that,” Dr. Dean said in an interview with “Fox News Sunday.” He said Americans are losing patience with the mission. “We’re not going to put up with terrorism in Iraq or anyplace else, but we can’t keep 140,000 brave Americans in Iraq indefinitely. Did not we learn this lesson in Vietnam?” the party official said.

However, Dr. Dean expressed doubt about a proposal to pull American troops out of Iraq by June. The plan, advanced by a former senator of South Dakota, George McGovern, is to be presented this week to a group of left-leaning lawmakers, the Congressional Progressive Caucus.

“Establishing an arbitrary deadline of next June, I think, is probably not the way it’s going to work,” Dr. Dean said.