Republican presidential candidate John McCain accused his Democratic rivals on Monday of making "reckless" promises they cannot keep by pledging speedy U.S. troop withdrawals from Iraq.

McCain's comments drew withering reactions from Democrats Barack Obama and Hillary Clinton, a measure of the deep divide they have over Iraq a day ahead of congressional testimony in Washington from the top American commander in Iraq, Gen. David Petraeus.

"I do not believe that anyone should make promises as a candidate for president that they cannot keep if elected," McCain said to applause in a speech to a Veterans of Foreign Wars convention.

Arizona Sen. McCain and his Democratic rivals, Illinois Sen. Barack Obama and New York Sen. Hillary Clinton, are all scheduled to be on Capitol Hill for the Petraeus testimony.

Petraeus is to provide an update on a five-year-old war that has cost more than 4,000 American lives and has been a major issue on the U.S. campaign trail.

McCain said U.S. forces should be given time for political reconciliation to take hold, saying the year-old "surge" overseen by Patraeus has led to dramatic reduction in violence and "opened the way for a return to something approaching normal political and economic life for the average Iraqi."

Clinton said McCain was pushing "four more years of the Bush-Cheney-McCain policy of continuing to police a civil war while the threats to our national security, our economy and our standing in the world mount."

"We simply cannot give the Iraqi government an endless blank check. It is time to end this war as quickly, as responsibly and as safely as possible," she said.

McCain used the word "reckless" four times to describe the Democrats' position, saying they are promoting an easier course of action to try to get an advantage in the election.

Obama had a withering response, saying McCain was "wrong about the war from the beginning."

WITHDRAWAL TALK

"It's a failure of leadership to support an open-ended occupation of Iraq that has failed to press Iraq's leaders to reconcile, badly overstretched our military, put a strain on our military families, set back our ability to lead the world and made the American people less safe," he said.

Obama and Clinton, engaged in a closely fought battle to determine which Democrat will face McCain in the November election, have vowed to begin pulling out U.S. troops from Iraq quickly after taking office in January 2009.

With security gains in Iraq still tenuous, Petraeus and Ambassador Ryan Crocker were expected to say in congressional testimony that further withdrawals of American troops should be put on hold after 20,000 come home by July.

This could leave more than 130,000 U.S. troops in Iraq through the end of the Bush administration.

McCain, ranking Republican on the Senate Armed Services Committee, said progress in Iraq has been undeniable thanks to the U.S. troop build-up, despite a recent surge in violence.

The former Vietnam prisoner of war has staked his candidacy on his support for the troop increase.

He said an Iraq that no longer needs American troops is a goal that is possible "perhaps sooner than many imagine" - while carefully avoiding a timetable for withdrawal.

"To promise a withdrawal of our forces from Iraq, regardless of the calamitous consequences to the Iraqi people, our most vital interests and the future of the Middle East, is the height of irresponsibility. It is a failure of leadership," he said.

Democratic National Committee Chairman Howard Dean fired back at McCain. "John McCain's irresponsible political attacks are not a substitute for a workable plan for the future of Iraq, something McCain has consistently refused to outline," Dean said.

McCain said the troop increase is working to bring security to Iraq. "There is no doubt about the basic reality in Iraq: we are no longer staring into the abyss of defeat, and we can now look ahead to the genuine prospect of success," he said.

The Iraq war remains a key issue in voters' minds ahead of the presidential election, but the souring economy is currently at the top of people's concerns.