President Bush threatened to veto legislation setting a date for a troop withdrawal from Iraq on Tuesday despite growing bipartisan calls in Congress for an end to U.S. participation in the war and sharp criticism of the Iraqi government.

As the Senate opened a new debate on the conflict, one of the president's staunchest supporters bluntly said the administration had pursued the wrong policy for years after toppling Saddam Hussein. "The strategy we had before was not the right strategy," said Christopher Bond, R-Mo. "We should have had a counterinsurgency strategy."

Asked later who bore responsibility for the error, Bond said, "Ultimately, obviously, the president."

Democrats said Bush's newest strategy was hardly a success, either.

Senate Majority Leader Harry Reid, D-Nev., said that since Bush ordered thousands more troops to Iraq last winter, "we've lost more than 600 troops, costing the American taxpayers more than $60 billion. The escalation has done nothing to bring the Iraqi government together. It's done absolutely nothing to lessen the violence in Iraq."

Two Democrats, Sens. Carl Levin of Michigan and Jack Reed of Rhode Island, back legislation to require a troop withdrawal to begin within 120 days, to be completed by the end of April 2008.

A vote is expected next week, and Reid said nearly all Democrats support the proposal. Republican Gordon Smith of Oregon is a supporter, as well, and Olympia Snowe, R-Maine, told reporters she may switch her position and vote for it, too.

House Speaker Nancy Pelosi said she would call for a vote on a similar measure by week's end.

The Senate proposal appears to be short of the 60 votes needed to overcome a threatened Republican filibuster. Bush's veto threat applied to any legislation that sets an arbitrary date for withdrawal "without regard to conditions on the ground or the recommendations of commanders."

"Setting a date for withdrawal is equivalent to setting a date for failure," he said in a written statement that employed terms similar to those he used earlier in the year when he vetoed legislation that set a target date for a withdrawal.

In a further sign of eroding GOP support, Sen. Elizabeth Dole, R-N.C., called for troops to come home next year.

"Simply put, our troops have been doing a great job, but the Iraqi government has not," said Dole, the latest Senate Republican facing the voters in 2008 to switch positions on the war. "Our commitment in Iraq is not indefinite, nor should the Iraqi government perceive it to be."

Also expected to come to a vote in the next two weeks is a plan to place into law recommendations from last winter's report from the bipartisan Iraq Study Group. The group called for removing all combat brigades not needed for training, force protection and counterterrorism by March 31, 2008. In an ominous sign for the White House, six Republicans have signaled support for the proposal, along with six Democrats.

Despite a steady procession of Republicans calling for a change in course, several GOP lawmakers warned against a precipitous withdrawal.

"I believe that our military in cooperation with our Iraqi security forces are making progress in a number of areas," said Sen. John McCain, R-Ariz., who recently returned from his sixth trip to the region. The GOP presidential candidate said he noted a dramatic drop in attacks in Ramadi in the western Anbar province.

Sen. Lindsey Graham, R-S.C., who accompanied McCain to Iraq, also cited progress since Gen. David Petraeus took command several months ago and the additional troops began arriving.

The Iraqis are "rejecting al-Qaida at every turn. I don't want the Congress to be the cavalry for al-Qaida," he said.

Graham was also part of a group of senators who met privately during the day with Stephen Hadley, the president's national security adviser, and Lt. Gen. Douglas Lute, a top adviser on the wars in Iraq and Afghanistan. The senator said afterward the White House is looking at new ways to hasten progress in two primary areas: destroying al-Qaida in Iraq and forcing the U.S.-backed government in Baghdad to make political progress.

But he quoted Bush's aides as saying the administration would oppose calls for a troop withdrawal.

Bush, who was in Cleveland, said issues related to troop strength "will be decided by our commanders on the ground, not by political figures in Washington, D.C."

He added, "I call upon the United States Congress to give General David Petraeus a chance to come back and tell us whether his strategy is working, and then we can work together on a way forward."

Petraeus is expected to make his report in September, but Bush also must give Congress an evaluation by July 15 on the progress made by the government of Prime Minister Nouri al-Maliki in several areas of political and economic change.

The 23-page report is expected to state that Iraq has not met or made substantial progress toward about half the targets set by Congress, and has made progress on or arguably achieved the others.

State Department spokesman Sean McCormack declined to list any benchmarks that have been met. But he conceded that the most prominent goals had not — enactment of legislation to allocate oil and gas revenue among the Iraqis or a law to address consequences of the mass firings of Baath Party members.

Bush's allies made clear their unhappiness with the government in Iraq.

"The central government's dysfunction is real. I'm not here to say that it's not," said Graham. "I am in many ways more depressed than I've ever been about political reconciliation in the short term."

McCain, Graham, Bond and others took turns on the Senate floor to warn of grave consequences if Democrats get their wish for a quick troop withdrawal.

At an afternoon news conference, Bond also brought up the question of overall strategy.

"Late last winter we confirmed General Petraeus unanimously to bring a new strategy. Republicans and Democrats said we needed a new strategy, and there's no question we did.

"The strategy we had before was not the right strategy. We should have had a counterinsurgency strategy. Unfortunately, General Garner lost that argument several years ago," he said a reference to the general who was installed as the first postwar governor of Iraq. Garner arrived in Iraq in April 2003 and was replaced the following month.

Asked, in retrospect, how long the House and Senate should have permitted an inadequate strategy to continue, Bond replied, "Congress was not running the war."