Sept. 15 (Bloomberg) -- President George W. Bush, explaining his latest strategy for Iraq, said his decisions on troop levels are guided by a principle that he called ``return on success.''

``The more successful we are, the more troops can return home,'' Bush said today in his weekly radio address.

Bush this week endorsed Army General David Petraeus's recommendations for a gradual drawdown of U.S. forces in Iraq over the coming year, so long as recent progress there continues. He said 5,700 troops would be withdrawn by the end of this year and as many as 30,000 by the middle of 2008.

``Security conditions are improving,'' Bush said today. ``The troop surge is working,'' he said, referring to his decision to add 30,000 troops this year, bringing the current force to about 169,000.

Democrats in Congress have rejected Bush's approach and vowed to press him to withdraw troops more quickly. While they have majorities in the House and Senate, they don't have enough votes to force such a change.

Representative Tom Lantos, a California Democrat who chairs the House Foreign Affairs Committee, said today that the troop increase was a strategic failure because Iraq's political leaders failed to move toward an accord that would end the violence.

``Strategically, the escalation has failed,'' Lantos said in the Democrats' weekly radio address. ``It was intended to buy time for Iraqi Prime Minister al-Maliki and the other Iraqi political leaders to find ways to move toward the one thing that may end this terrible civil conflict: a political settlement. As best we can see, that time has been utterly squandered.''

Government Loses Support

Iraq's political process suffered a blow today when lawmakers loyal to anti-American cleric Moqtada al-Sadr announced their withdrawal from the government, the Associated Press reported from Baghdad.

That decision leaves Prime Minister Nuri al-Maliki 30 seats short of a majority and complicates U.S.-backed efforts to win parliamentary approval of power-sharing legislation including measures that would grant all groups a share of oil revenue and ease curbs that prevent former Saddam Hussein supporters from getting back their government jobs, AP said.

Meanwhile, a car bomb today outside a bakery in southwestern Baghdad killed at least 11 people in a crowd lined up to buy bread as the daytime Ramadan fast was about to end, AP said.

Petraeus, Crocker

In testimony to Congress this week, Petraeus, the top U.S. commander in Iraq, and Ryan C. Crocker, the U.S. ambassador there, said that some progress is being made on security, even as the central government of Iraq remains deadlocked on broader political compromises.

Lantos today said that, while lawmakers respect Petraeus and Crocker, the two officials were given ``an impossible task: restore credibility to a discredited policy.''

``The administration's myopic policies in Iraq are deeply flawed,'' Lantos said. ``And their latest assessment of the situation there contrasts sharply with the deeply pessimistic reports of the non-partisan Government Accountability Office and the Independent Commission on the Security Forces of Iraq.''

``The United States needs a new direction in its policy on Iraq,'' Lantos said. `We need to get out of Iraq, for that country's sake as well as our own.''

To contact the reporter on this story: Holly Rosenkrantz in Washington at hrosenkrantz@bloomberg.net

Last Updated: September 15, 2007 15:18 EDT