As the House prepared to vote Thursday on a supplemental war spending bill, the White House warned that President Bush would veto the measure.

The White House said certain policy provisions in the bill would “tie the hands of our military commanders and impose an artificial timeline for withdrawal.”

The legislation calls for the withdrawal of troops to begin within 30 days with a nonbinding “goal” of completion within 18 months.

“Precipitous withdrawal from Iraq would embolden our enemies and confirm their belief that America will not stand behind its commitments,” the White House said.

House Appropriations Chairman David R. Obey , D-Wis., on Wednesday called the time frame “hardly precipitous.”

Although Democrats have repeatedly tried to force an end to the war, they have been stymied by Bush’s willingness to veto bills in the past. At a press conference Thursday morning, House Speaker Nancy Pelosi , D-Calif., said that she was not disappointed by her members.

“In the House of Representatives we have passed every resolution that we put forward to have a time certain or a goal for redeploying of our troops out of Iraq,” she said. “I’m very pleased with what we have been able to do in the House of Representatives and that’s what I am responsible for.”

The White House also objects to Democrats’ plan to include a 13-week extension of unemployment benefits in the spending bill, along with a major expansion of GI Bill education benefits for benefits and language that would block new Medicaid regulations that shift costs from the federal government to the states.

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