KANSAS CITY, Mo. — Republican presidential candidate John McCain said yesterday that calls from his Democratic rivals to withdraw American forces from Iraq stand as a “failure of leadership” as they are making promises they cannot keep. Senator Obama said the failure rests with Mr. McCain’s support for an open-ended occupation of Iraq.

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

Pulling out now would jeopardize recent gains, Mr. McCain said. “I do not believe that anyone should make promises as a candidate for president that they cannot keep if elected,” Mr. 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.”

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