President Bush's top military and political advisers on Iraq will warn Congress on Monday that significant changes to the war strategy will jeopardize the limited security and political progress so far, The Associated Press has learned.

Ambassador Ryan Crocker will join Gen. David Petraeus, the top commander in Iraq, in recommending maintaining President Bush's troop increase, seeing it as the only viable option to prevent further chaos in the country and region, U.S. officials said.

Crocker and Petraeus planned to meet on Sunday to go over their remarks and responses to the expected sharp questioning from lawmakers Monday and Tuesday. They will not consult Bush or their immediate bosses before their appearances, in order to preserve the "independence and the integrity of their testimony," said one official.

The two had lengthy discussions with the president, as well as Defense Secretary Robert Gates and Secretary of State Condoleezza Rice, during Bush's visit to Iraq on Labor Day.

The officials spoke on condition of anonymity because they were discussing internal deliberations.

Crocker is pushing for political change where progress has been elusive and the administration's options are limited, given the fragile Shiite-led government of Prime Minister Nouri al-Maliki.

Yet the diplomat will say that as poorly as al-Maliki's government has performed, it would not be advisable for the U.S. to support new leadership or lobby for a different coalition of Iraq's fractious populations, according to one official.

Both Crocker and Petraeus will say the buildup of 30,000 troops, bringing the current U.S. total to nearly 170,000, has achieved some success and is working better than any previous effort to quell the insurgency and restore stability, according to officials familiar with their thinking.