Washington, D.C. ? On the eve of a trip today to Central and South America, Defense Secretary Robert Gates postponed his travel plans to help the White House assemble a progress report on the situation in Iraq.

The move comes amid growing pressure on the Bush administration to withdraw U.S. troops from Iraq. The political climate for the war has grown markedly worse in recent days, with a group of senior Republicans changing their stance on Iraq and now leaning toward a withdrawal of troops.

Congress has given the Bush administration two deadlines to report on the situation in Iraq and assess whether it is improving. The first of those deadlines is Sunday, and the Pentagon said in a statement that Gates’ participation is needed in policy meetings.

Also this week, Congress is set to begin consideration of the defense spending bill, a debate that is sure to be dominated by discussion of Iraq.

The statement said Gates’ long-planned trip to El Salvador, Colombia, Peru and Chile will be rescheduled.