The top U.S. officials in Iraq will testify on the war for a second day to Congress on Wednesday as the Bush administration makes its case against a big troop pull-out.

Gen. David Petraeus, the U.S. commander in Iraq, and Ambassador Ryan Crocker will argue the United States risks losing ground to al Qaeda in Iraq if it withdraws too many troops out of the war zone too quickly.

Leading Democrats, including the party's contenders in the November presidential election, advocate beginning a process to withdraw U.S. forces from Iraq and to focus more attention on fighting al Qaeda in Afghanistan and Pakistan.

Petraeus told the Senate on Tuesday he wanted to halt troop withdrawals after a current drawdown ends in July, leaving around 140,000 U.S. troops in Iraq. President George W. Bush has said he would back such a recommendation.

Petraeus and Crocker will appear on Wednesday before the House of Representatives' committees on armed services and foreign affairs.

Bush plans to meet members of Congress once the testimony is over and to give "a wide-ranging speech on a variety of issues" related to Iraq on Thursday, White House spokeswoman Dana Perino said.

"What the president is focused on is making sure that our troops have what they need to succeed and that we're supporting the overall mission so that we can create a more stable Iraq, one that can sustain, govern and defend itself and one that can be an ally in the war on terror," Perino said.

U.S. officials have said Bush is expected to announce, perhaps as soon as Thursday, that U.S. soldiers' tours in Iraq and Afghanistan will be cut back to one year from 15 months.

The announcement of a shortened combat tour could help the Bush administration signal progress in the war, now back among the top concerns of American voters ahead of the election.

Democrats, however, have already cast the progress report from Petraeus and Crocker as a sign the Bush administration has no plan to end the conflict.

They say that while the "surge" of extra troops into Iraq last year helped reduce violence, it did not yield the political progress among Iraqi factions that Bush promised.

Describing security gains in Iraq as fragile, Petraeus said he wanted 45 days of consolidation once the current drawdowns are complete and his staff would then begin looking at when further withdrawals could take place.