President Bush has endorsed a plan to put an indefinite hold on further troop withdrawals after July.

On Thursday, the president also announced that U.S. troop combat tours would cut be from 15 months to 12 months, and said Army units will have a year of rest for every year of combat.

Gen. David Petraeus this week told Congress he has recommended a 45-day moratorium on troop movements following a series of withdrawals due to end in July. Only after that, he said, would he make further recommendations on when to drop troop levels further.

Bush said he fully backs that plan, citing news of ongoing success in Iraq but concerns of continued threats from insurgents, Al Qaeda in Iraq and Iran.

"I've told him he'll have all the time he needs," Bush told reporters, speaking at the White House Cross Hall.

But the top House and Senate Democrats said the moves do not go far enough to ease the burden on U.S. forces, fight Al Qaeda in Afghanistan and to avert domestic economic crisis.

"The president has taken us into a failed war. He's taken us deeply into debt. And ... that debt is taking us into recession. We need some answers from the president," House Speaker Nancy Pelosi said, speaking to reporters in the Capitol shortly after Bush ended his remarks.

"He is just dragging this out so he can put it at the doorstep of the new president of the United States," said Pelosi, D-Calif. Pelosi was joined in her criticism of Bush by Senate Majority Leader Harry Reid, D-Nev.

In his remarks, Bush said descriptions of Petraeus' recommendations as a "pause" were incorrect.

"That's misleading because none of our operations in Iraq will be on hold," Bush said.

Bush announced his plans to send another 30,000 more combat troops to Iraq in January 2007, with the surge beginning in earnest about one year ago. Following last September's report from Petraeus and U.S. Ambassador to Iraq Ryan Crocker, Bush announced he would begin bringing home the extra troops, setting July as the end-point for the withdrawal of the surge forces.

A sore point for Democrats, military planners have indicated that troop forces in July would stand at about 140,000, about 10,000 more than where they stood before the surge.

While noting continued challenges to U.S. efforts in Iraq, Bush sounded an optimistic tone for Iraq and the likelihood of success and said the troop surge made that success possible.

"With the surge, a major strategic shift has occurred. Fifteen months ago, America and the Iraqi government were on the defensive. Today, we have the initiative. ... " Bush said. "Americans were worried about the prospect of failure in Iraq. Today, thanks to the surge, we've renewed and revived the prospect of success."

But since the surge began, the Pentagon hiked Army active-duty combat tours from 12 months to 15 months as a result of force strains, a move that affected tens of thousands of soldiers.

Bush's combat tour-length and rest announcement was aimed at soothing stressed soldiers and families, he said.

"To ease the burden on our troops and their families, I have directed the secretary of Defense to reduce deployment lengths from 15 months to 12 months for all active Army soldiers deploying to Central Command area of operations," Bush said. Central Command -- or CentCom -- encompasses Iraq, the Middle East and Afghanistan.

"We'll also ensure that Army units will have at least a year home for every year in the field," Bush said. "Our nation owes a special thanks to the soldiers and families who supported this extended deployment. We owe a special thanks to all that served the cause of freedom in Iraq."

The Army said the changes would be effective for those deploying on or after Aug. 1. Those currently serving 15-month tours would have to serve out the full length of their tours. The one-year rest requirement would kick in for those units deployed starting in August.

This week, Petraeus told Congress it's too early to talk about future drawdowns because the situation in Iraq remains fragile, and that while security has improved and Iraqi forces are shouldering more of the fight against extremists, Iraq still could descend again into chaos. Despite claims he would not make another decision for six months, Petraeus told FOX News that he has not established any timeframe to make a determination for further drawdowns.

Bobby Muller, president of Veterans for America, said waiting until after the summer to return to 12-month tours will do nothing to relieve the burden on troops currently on 15-month stints, including some who are not scheduled to return home until the summer of 2009.

"Almost half of the active-duty Army's frontline units are currently deployed for 15 months. Three of these units are on their fourth tour. Almost all have served at least twice," he said. "This is the group of soldiers that has borne an immense, disproportionate burden from our wars. This is the group of soldiers that desperately needs a break — now."

Bush had breakfast with Petraeus and Crocker in his private dining room, capping two days of televised exchanges on Capitol Hill that the two had with lawmakers, including the three senators vying to become next occupant of the Oval Office: Republican John McCain and Democrats Barack Obama and Hillary Rodham Clinton.

The Associated Press contributed to this report.