The legislation also would require Bush to seek congressional approval for any military operations in Iran.

The Senate, meanwhile, could begin floor debate on Iraq as early as next week. Sens. Joseph Biden , D-Del., and Carl Levin , D-Mich., have proposed a resolution that would call for combat troops to come home by March 2008.

As Democrats finalized their spending plan for this year, White House chief of staff Joshua Bolten told Senate Republican leaders that the administration will need additional funding to pay for the influx of troops to Iraq.

The Pentagon initially estimated the 21,500 troops would cost $5.6 billion through Oct. 1. But 6,000 more personnel will be needed to provide support to the combat units, according to GOP aides.

The administration also might amend its funding request in order to provide more money for Afghanistan.

The White House is expected to offer to trim other parts of the 2007 war spending request such as the controversial V-22 tilt-rotor aircraft to offset the money needed. Bolten did not offer a specific figure for the support troops, the aides said.

Also on Thursday, an influential Senate Democrat floated the idea of cutting $20 billion from Bush's request for military operations next year in Iraq and Afghanistan, only to be swiftly overridden by his colleagues.

The trial balloon floated by Budget Committee Chairman Kent Conrad would have trimmed Bush's $142 billion war budget for 2008 by about one-seventh in keeping with cost estimates by the nonpartisan Congressional Budget Office.

Conrad's idea would have applied to the next budget year beginning Oct. 1 - a separate issue from the debate over Bush's $100 billion request for immediate supplemental war funding.

But it raised concerns among Democrats sensitive to any accusations of shorting funding for troops in battle.

"Our caucus feels strongly that we should go with the president's numbers" on 2008 war costs, Conrad said.

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