WASHINGTON (AP) - President Bush, under growing political pressure, agreed to negotiate with Congress on a war-spending bill that sets benchmarks for progress in Iraq.

The turnabout in Bush's position came as Republicans expressed anxieties about the war and the House was expected to pass legislation that would cut off funding for U.S. troops as early as July.

Bush said he would veto the measure. "We reject that idea. It won't work," the president said, speaking to reporters at the Pentagon after a briefing on Iraq and Afghanistan.

The bill voted on Thursday is opposed by nearly all Republicans and unlikely to survive in the Senate. But House Democratic leaders say the measure shows they refuse to back down in challenging President Bush on a deeply unpopular and costly war.

"The president refuses to listen to the American people who want this war to end," said House Speaker Nancy Pelosi, D-Calif.

Bush pressured Iraqi leaders to move swiftly on a number of long-pending measures, including legislation to share Iraq's oil wealth, hold provincial elections and update the constitution.

"They have got to speed up their clock," the president said. Washington is unhappy that Iraq's parliament plans to take a two-month vacation this summer in the midst of the war.

Bush's willingness to put benchmarks in a war-funding bill represented a shift by the president.

"One message I have heard from people of both parties is that benchmarks make sense and I agree," Bush said. He said his chief of staff, Joshua Bolten, would talk with congressional leaders "to find common ground" on benchmarks.

White House officials decided Bush, after refusing to discuss his negotiating stand, should change course and declare what he is for since he been emphatic about what he is against.

The Democrats' bill in the House would provide the military with $42.8 billion to keep operations going through July, buy equipment and train Iraqi and Afghan security forces. Congress would decide shortly before its August recess whether to release an additional $52.8 billion for war spending through September.

A dozen or so members in Congress are attempting to strike a bipartisan compromise. Few have come forward with concrete plans - perhaps out of reluctance to champion a proposal until they know it can succeed. None of the proposals put in plain view have picked up steam.

"We'll see what happens," said Rep. Bud Cramer, D-Ala. "A lot of us are coming together across the aisle. We're under the radar now, but we're meeting."

Many Republicans have grown nervous on the war.

Two Republicans - Reps. Frank Wolf of Virginia and Michael McCaul of Texas - circulated a letter along with Democrat Mark Udall of Colorado urging their colleagues to co-sponsor legislation that would put in place recommendations from the independent Iraq Study Group.

One of the 79 suggestions from the bipartisan group in December was reducing U.S. "political, military or economic support" for Iraq if the Baghdad government could not make substantial progress toward providing for the country's security. The report suggested an urgent diplomatic attempt to stabilize Iraq and allow the withdrawal of most U.S. combat troops by early 2008.

Bush said Congress should give his buildup of more than 20,000 troops a chance to work.

Gen. David Petraeus, the top U.S. commander, is to report to Bush in September on the effectiveness of the buildup.

"Why don't we wait and see what happens," the president said. "Let's give this plan a chance to work. Let's stop playing politics."

Bush said the House Democrats' plan to pay for the war only through July was "haphazard, piecemeal funding."

Of the five brigades of additional forces being sent to Iraq, Bush said three are already settled there, the fourth has just entered Baghdad and the fifth will arrive in mid-June.

"Al-Qaida is responding with their own surge. Al-Qaida is ratcheting up their own campaign of high-profile attacks," Bush said.

Rep. Tom Davis of Virginia was one of 11 GOP lawmakers who met with Bush and his top aides Tuesday afternoon.

"We asked them what's Plan B," Davis said. "We let them know that the status quo is not acceptable." Davis said the president responded that if he began discussing a new strategy, his current one never would have a chance to succeed.

Several GOP senators sought to find their own solution.

Last week, Sen. John Warner, R-Va., raised hopes when he said he had an idea that had enough support to override a veto. Warner said his proposal would pressure the Iraqi government to take more initiative on political and security reforms. He declined to offer more specifics.

On Wednesday, Warner said he was reassessing in light of the new House proposal.

Sens. Susan Collins, R-Maine, and John Sununu, R-N.H., said they are open to considering conditions on foreign aid to Iraq if the Baghdad government fails to meet certain benchmarks.

Meanwhile, Vice President Dick Cheney defended the Bush administration's recent decision to extend military deployments as "vital to the mission" during a visit to U.S. troops near Tikrit.

He vowed to "stay on the offensive" despite growing public opposition in the United States to the war and efforts by the Democratic majority in Congress to restrict spending.

Cheney, who was defense secretary in the first Bush administration, spent the night on the base, about seven miles from Tikrit, Saddam's former hometown and an area populated mostly by minority-party Sunnis.

It was the first time Cheney spent the night in Iraq, and his whereabouts was closely guarded by the White House until Thursday's speech to the troops.

The vice president is on a weeklong tour of the Middle East that will also take him to Saudi Arabia, Egypt and Jordan. On Friday, he will visit U.S. troops on the aircraft carrier USS John C. Stennis in the Persian Gulf.

Gen. Benjamin R. (Randy) Mixon, commander of coalition forces in northern Iraq, told reporters that since President Bush announced his military buildup earlier this year, some al-Qaida and other militants have migrated from Baghdad to other areas of Iraq, including some in northern areas under his command.

As to the extensions of duty on troops at Camp Speicher, Mixon said, "They understand perfectly the reason the mission's been extended. The morale is good, in terms of staying focused on the mission. They want to know the exact day their going back. That gives them something to focus on."

"This budget battle has been particularly frustrating to us," Mixon said of congressional efforts to set timetables for troop withdrawals.

"We cannot stay here forever, we all know that," he said. He said the solution to the problem is to keep training the Iraqi army and police.

Specialist Eric Emo, 23, of Sedalia, Mo., whose Army unit is based in Fort Riley, Kan., said most of his fellow soldiers are unhappy about the deployment extensions, but understand the need for it.

In terms of hostile activity, he said, "conditions around here have gotten a lot worse." He said there has been a particularly sharp increase in the number of roadside bombs.

Associated Press Writer Tom Raum contributed to this report.