WASHINGTON – A leading Republican senator and prospective presidential candidate said yesterday that the war in Iraq has destabilized the Middle East and is looking more like the Vietnam conflict from a generation ago.

Senator Hagel of Nebraska, who received two Purple Hearts and other military honors for his service in Vietnam, reiterated his position that America needs to develop a strategy to leave Iraq.

Mr. Hagel scoffed at the idea that American troops could be in Iraq four years from now at levels above 100,000, a contingency for which the Pentagon is preparing.

“We should start figuring out how we get out of there,” Mr. Hagel said on “This Week” on ABC.” But with this understanding, we cannot leave a vacuum that further destabilizes the Middle East. I think our involvement there has destabilized the Middle East. And the longer we stay there, I think the further destabilization will occur.”

Mr. Hagel said “stay the course” is not a policy. “By any standard, when you analyze 2 1/2 years in Iraq … we’re not winning,” he said.

President Bush was preparing for separate speeches this week to reaffirm his plan to help Iraq train its security forces while its leaders build a democratic government. In his weekly Saturday radio address, Mr. Bush said the fighting there protects Americans at home.

Polls show that the public is growing more skeptical about Mr. Bush’s handling of the war.

In Iraq, officials continued to craft a new constitution in the face of tonight’s deadline for parliamentary approval. They missed the initial deadline last week.

Other Republican senators appearing on Sunday news shows advocated remaining in Iraq until the mission set by Mr. Bush is completed, but they also noted that the public is becoming more and more concerned and needs to be reassured.

[No sooner had the Associated Press attributed Mr. Hagel’s remarks to a “leading Republican senator and prospective presidential candidate” than the characterization was disputed by the Web log Power Line, which follows, among other issues, heartland politicians. “What exactly makes Chuck Hagel a ‘leading Republican senator’?” Power Line asked. “Not seniority; he is a second-termer. Not any official responsibilities; Hagel is not a member of the Senate leadership, nor does he chair a Senate committee. Not legislative accomplishment or influence; Hagel has little noteworthy legislation to his name, and is more often an eccentric voice – e.g., in his call for reinstatement of the draft – than an influence on his fellow Senators.” It cast doubt that he could be a “prospective presidential candidate” as a Republican.]

Senator Allen, a Republican of Virginia, another possible candidate for president in 2008, disagreed that America is losing in Iraq. He said a constitution guaranteeing basic freedoms would provide a rallying point for Iraqis.

“I think this is a very crucial time for the future of Iraq,” Mr. Allen said, also on ABC. “The terrorists don’t have anything to win the hearts and minds of the people of Iraq. All they care to do is disrupt.”

Mr. Hagel, who was among those who advocated sending two to three times as many troops to Iraq when the war began in March 2003, said a stronger American military presence is not the solution today.

“We’re past that stage now because now we are locked into a bogged-down problem not unsimilar, dissimilar to where we were in Vietnam,” Mr. Hagel said. “The longer we stay, the more problems we’re going to have.”

Mr. Allen said that unlike the communist-guided North Vietnamese who fought America, the insurgents in Iraq have no guiding political philosophy or organization. Still, Mr. Hagel argued, the similarities are growing.

“What I think the White House does not yet understand – and some of my colleagues – the dam has broke on this policy,” Mr. Hagel said. “The longer we stay there, the more similarities [to Vietnam] are going to come together.”

The Army’s top general, General Peter Schoomaker, said Saturday in an interview with the Associated Press that the Army is planning for the possibility of keeping the current number of soldiers in Iraq – well over 100,000 – for four more years as part of preparations for a worst-case scenario.

Senator Graham, a Republican of South Carolina, said American security is tied to success in Iraq, and he counseled people to be patient.

“The worst-case scenario is not staying four years. The worst-case scenario is leaving a dysfunctional, repressive government behind that becomes part of the problem in the war on terror and not the solution,” Mr. Graham said on “Fox News Sunday.”