BAGHDAD, Iraq - U.S. Sen. Hillary Rodham Clinton expressed doubt Saturday that Iraq's government would follow through with its promises to secure Baghdad as she met with top Iraqi officials and American commanders.

It was the third trip to Iraq for Clinton, a Democrat from New York who is considering running for president, and comes amid opposition from the Democratic-controlled Congress to President Bush's plans to send in 21,500 more troops to stop the rampant violence.

"I don't know that the American people or the Congress at this point believe this mission can work," she told ABC News in Baghdad. "And in the absence of a commitment that is backed up by actions from the Iraqi government, why should we believe it?"

Noting she had to travel wearing body armor and surrounded by soldiers and security guards, Clinton called the situation in Iraq "heartbreaking."

"This is my third trip here. I've seen the violence and security problems increase, not decrease," she said, calling on Bush to start withdrawing U.S. troops.

"That would really demonstrate to the Iraqis that we don't have an open-ended commitment," she said. "We are not going to be here providing protection for their leaders, which we do. We are not going to be here standing by and trying to be called in from time to time as they see fit. That is not in the cards."

Clinton, who was making a one-day visit to the country, spoke to ABC exclusively after meeting with the two top military commanders in Iraq, U.S. Gen. George Casey and Lt. Gen. Ray Odierno, according to the network.

She was traveling with U.S. Sen. Evan Bayh, D-Indiana, who opted out of the 2008 race, and Rep. John McHugh, a Republican from upstate New York. They also planned to travel to Afghanistan.

The three, all members of armed services committees, also met with Iraqi Prime Minister Nouri al-Maliki.

"I'm skeptical that the Iraqi government will do what they have promised to do, and that I think is the concern of all of us who have heard this before," she said, referring to earlier security efforts that have failed to stop the sectarian attacks that have been increasing since the Feb. 22 bombing of a Shiite shrine in Samarra.

Clinton, who opposes Bush's plans to send more U.S. troops to Iraq, last traveled to Iraq in February 2005 with Sen. John McCain, a Republican presidential contender.

Clinton had planned to meet with the Army's 10th Mountain Division -- which is based in New York and deployed in both Iraq and Afghanistan -- at their base in Baghdad but the visit was canceled due to bad weather, the U.S. military said.