Fallujah, Iraq ? Defense Secretary Robert Gates, on an unannounced trip to Iraq, delivered a sharp message to the country’s political leaders Thursday: The U.S. military’s commitment to the war is not open-ended.

“The clock is ticking,” Gates told reporters, saying he will warn Iraqi officials that they must move faster on political reconciliation. “I know it’s difficult, and clearly the attack on the council of representatives has made people nervous, but I think that it’s very important that they bend every effort to getting this legislation done as quickly as possible.”

A suicide bomber infiltrated the parliament building in the heavily fortified Green Zone a week ago, dealing a blow to the U.S.-led effort to pacify the capital’s streets.

Prime Minister Nouri al-Maliki called the violence in Baghdad an “open battle.”

Gates, traveling to Iraq for the third time in four months, took a decidedly stronger tone this time, reflecting U.S. frustration and the political tumult in Washington, where President Bush and Congress are deadlocked over whether to set an end date for the war.

Since January, when Bush announced his new strategy for the Iraq war – featuring a troop buildup and a renewed push for economic development and political progress – Gates and other senior administration officials have frequently and publicly reminded the Iraqis that they must act quickly to settle their differences. They have attempted to strike a balance between pressuring the Iraqis to reconcile and reassuring them that the U.S. military will not abandon them while they struggle to avert a full-scale civil war.

Gates said again Thursday that the Washington debate has been helpful in letting the Iraqis know that American patience with the war is ebbing. Democrats have seized on those remarks to bolster their arguments that there must be a deadline for the Pentagon to begin withdrawing troops from Iraq.

Speaking at a town hall-style gathering in Ohio on Thursday, Bush reiterated his opposition to any timetable for a troop withdrawal.

“If you’re a young commander on the ground, or an Iraqi soldier, and you’ve been tasked with a mission to help provide security for a city, and an enemy hears that you’re leaving soon, it affects your capacity to do your job,” Bush said.

Gates said the Iraqis must, as quickly as possible, push through legislation on political reconciliation and the sharing of oil revenues among the Sunnis, Shiites and Kurds.

“It’s not that these laws are going to change the situation immediately, but I think … the ability to get them done communicates a willingness to work together,” he said.

Those efforts, Gates said, would, in turn, create an environment in which violence could be reduced. But he acknowledged, “I’m sympathetic with some of the challenges that they face.”