Defense Secretary Robert Gates said Thursday that extending deployments of U.S. troops now in Iraq beyond the current 15 months was a "worst-case scenario" and that he didn't anticipate it happening.

He also told a Pentagon news conference he couldn't say how long American forces would have to stay at increased levels in the effort to secure Baghdad.

Military deployments were recently extended to 15 months from 12 months. He said it was his hope to move as soon as possible back to 12-month deployments, with a year at home, and then eventually to 12-month terms with two years at home.

Gates was asked about a recent surge in violence and increased attacks on U.S. troops.

"The reason for the spike in violence is ... our troops and the Iraqi troops are going into areas where they haven't been for some time. They anticipated there would be a high level of combat," Gates said.

Asked about the prospects for leaving U.S. troops in Iraq at their current high levels, Gates said, "We'll just to have to wait and see the progress of these offensives."

Gen. Peter Pace, outgoing chairman of the Joint Chiefs of Staff, said the current U.S.-led offensive was "exactly what needs to be done." He said it "buys time for the Iraqi government. ...This is the right thing to do."

He noted that decisions would be made after reports on progress are made in September by Gen. David Petraeus, the top U.S. commander in Iraq, and Ryan Crocker, the U.S. ambassador there.

It was Pace's first exchange with reporters since the administration's surprise decision earlier this month to replace him.

Pace, whose current term ends Oct. 1, said he intended to remain on the job until then and would continue to "give my best military advice."

"I am chairman and I'm going to be chairman until midnight the 30th of September," he said, promising to "remain focused."

Bush nominated Navy Adm. Michael Mullen to succeed Pace. "He'll be as honored to serve as I have been," Pace said.

"We can expect that there is going to be tough fighting ahead. There is an expectation that this surge is going to result in more contact and more casualties," he said.

Gates was asked about progress of President Bush's military buildup in getting Iraq to govern and defend itself.

He said he was satisfied with progress on "the military side, the security side" but that it would "take longer" for Iraq to meet its political and economic commitments, including a plan to share oil revenues and political reconciliation among Iraq's Sunnis, Shiites and Kurds.

Congress ordered a first report on progress in Iraq to be completed by July 15 and a second one by mid-September.

By then, Petraeus and Crocker will have made their own assessment on whether to maintain the U.S. troop build up or start reducing troop levels.

More than 3,540 American troops have died since the war began in 2003. On Thursday, 14 American troops died in multiple attacks, including five killed in a single roadside bombing in Baghdad.

Gates and Pace said the military was reaching out to groups who in the past have been attacking U.S. troops and even arming some of them.

"Trying to bring some level of peace to Iraq is trying to persuade some people who have been fighting to stop fighting," Gates said. "We are going to be talking to people who not long ago might have been shooting at us."

Pace acknowledged there was a risk involved in arming such groups. "But I think there's a greater risk of missed opportuinties ... that we should sieze on those opportunities," Pace said.