Washington ? Military commanders in Iraq are developing a plan to move as many as 5,000 U.S. troops with armored vehicles and tanks into Baghdad in an effort to quell escalating violence, defense officials said Thursday.

As part of the plan, Defense Secretary Donald H. Rumsfeld on Thursday extended the tours of some 3,500 members of the 172nd Stryker Brigade Combat Team. The unit, which has been serving in northern Iraq, was scheduled to be leaving now, but instead, most of its 3,900 troops will serve for up to four more months. It was unclear whether the unit would go to Baghdad.

Under the plan to bolster security in Baghdad, U.S. troops would be teamed with Iraqi police and army units and make virtually every operation in the city a joint effort, one military official said. Another said movement of some troops into Baghdad had already begun.

At the same time, the Pentagon signaled plans to maintain or possibly increase the current level of about 130,000 troops in Iraq, by announcing that roughly 21,000 Army soldiers and Marines have been told they are scheduled to go to Iraq during the current 2006-08 rotation.

Combined with two previous announcements of about 113,000 U.S. service members scheduled for the rotation period, this could bring the number of U.S. troops there to 134,000, if all are deployed.

Military commanders have said deployments depend on conditions in Iraq. But the latest announcement calls into question whether the Pentagon could significantly reduce troop levels in Iraq by year’s end as commanders had hoped.

As part of the Baghdad security plan, all flights out for soldiers currently at the end of their deployment were canceled as of Tuesday, as commanders wrestled how to supply troops for the effort, a third official said.

All spoke on condition of anonymity because the plan had not been finalized.

Rumsfeld, meanwhile, met privately with lawmakers on Capitol Hill throughout the day Thursday to discuss funding needed for troops and the replacement or repair of equipment damaged in combat. House and Senate Republicans are weighing next year’s defense spending bills amid reports that Army units are woefully ill-equipped and need billions of dollars to recover from the war.

“There is no question that resetting the force after the heavy usage that’s occurred costs money and will have to be funded in supplementals for a period of time,” said Rumsfeld, who predicted that funds may be needed for up to three years after the war ends.

President Bush broadly outlined a plan to increase U.S. and Iraqi forces in Baghdad during Tuesday’s visit to Washington by Iraqi Prime Minister Nouri al-Maliki. But little detail was provided.

Officials said it would involve shifting some U.S. forces to the capital from other locations in the country. There were about 30,000 U.S. troops in Baghdad before the new plan.

Assembling more troops and armor in Baghdad is aimed at calming violence that has only increased in the capital since mid-June, when al-Maliki launched a broad security crackdown.

The plan includes moving about four companies of military police, or about 400 soldiers, to Baghdad, along with the remainder of a reserve force that had been in Kuwait – equaling about another 400 troops.