Kansas City, Mo. ? Republican presidential candidate John McCain said Monday that calls from his Democratic rivals to withdraw U.S. forces from Iraq stand as a “failure of leadership” as they are making promises they cannot keep.

Democrat Barack Obama said the failure rests with McCain’s support for an open-ended occupation of Iraq.

Addressing the Veterans of Foreign Wars, McCain criticized Obama and Democratic Sen. Hillary Rodham Clinton and insisted that last year’s U.S. troop buildup in Iraq brought a glimmer of “something approaching normal” there, despite a recent outbreak of heavy fighting and a U.S. death toll that has surpassed 4,000.

Pulling out now would jeopardize recent gains, McCain said.

“I do not believe that anyone should make promises as a candidate for president that they cannot keep if elected,” McCain told the crowd of about 130 people, mostly veterans.

“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,” he said. “It is a failure of leadership.”

He took a brief tour of the National World War I Museum afterward.

McCain, the presidential nominee-in-waiting, is closely tied to the unpopular, 5-year-old war. McCain was a vocal advocate of the troop increase strategy eventually adopted by President Bush, and is seeking to convince people the strategy is working. He also argued that Iraq will need more money and aid for reconstruction.

Clinton and Obama, still battling for the Democratic presidential nomination, dispute the claims of success, arguing the war has failed to make the United States safer.

“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,” Obama said, using McCain’s own words against him.

Clinton chastised McCain’s Iraq strategy as “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,” she said. “It is time to end this war as quickly, as responsibly, and as safely as possible.”

Debate will intensify this week as Gen. David H. Petraeus, the top commander in Iraq, and Ambassador Ryan C. Crocker testify to Congress. Clouding their testimony is fighting that erupted late last month as U.S.-trained Iraqi forces attempted to oust Shiite militias from Basra in southern Iraq.

For his part, McCain suggested the Democrats’ promise to withdraw troops was motivated by ambition rather than honesty.

People deserve a candid assessment of progress in Iraq as well as of the serious difficulties that remain and of the consequences of hasty withdrawal, McCain said.

McCain warned against the swift withdrawal of troops advocated by Obama and Clinton, saying Iraq could quickly become a terrorist haven.