The U.S. is ready to defend its interests in the Middle East for decades to come, even though the Iraq war has been tougher than expected, Defense Secretary Robert Gates said Friday.

Gates made the comments at a ceremony where Navy Adm. William Fallon was formally installed as the new head of U.S. Central Command, putting him in charge of American forces in the Middle East and Central Asia. Gates said the United States will continue to stand by its allies in the region.

The U.S is "dedicated to strengthening those commitments and defending our interests for the decades to come. And we will do all in our power to protect and defend our homeland," he said.

Fallon replaced Gen. John Abizaid, who led Central Command since 2003 but is leaving as part of a reshuffling of Mideast military commanders by President Bush. Besides Iraq, Fallon will also oversee the war in Afghanistan, where the U.S. and its allies are expecting a fresh Taliban offensive as the weather warms this spring.

"I am sure that General Abizaid would agree that not everything has gone as planned, as expected, or as hoped," Gates said in remarks to the large, mostly military crowd. "This is the nature of war."

He said Abizaid realized early on that the fight against jihadist extremism "would be a long and difficult endeavor."

Fallon, 62, takes over the job in the midst of a raging congressional debate over the administration's strategy in Iraq, even as more U.S. troops pour into Baghdad as part of Bush's plan to bring security and stability to the country.

"We need you again. You are one of the best strategic thinkers in uniform today. You are exactly the right person for this post," Gates said.

His comments came a day after a Democratic-led House committee, on a largely party line vote, approved legislation containing a Sept. 1, 2008, deadline for the withdrawal of troops from Iraq. Democrats leading the push to end the war, which has claimed the lives of more than 3,200 U.S. troops, are facing a threatened veto threat.

A less aggressive pullout plan offered by Democrats was turned back in the Senate, after it came 12-votes shy of the needed 60 votes to pass.

During Abizaid's tenure, Gates said, Iraq held three successful elections and its economy has grown. At the same time, however, the U.S. military and its coalition partners have struggled to tamp down the debilitating sectarian strife and quell a stubborn insurgency. Efforts to rebuild the country have been plagued with problems.

In recent weeks, however, there appear to be some indications of progress, even though only two of the five brigades planned for the troop increase have deployed to Iraq. The remaining three will deploy one per month. The buildup includes about 21,500 U.S. forces and several thousand additional support troops and military police.

When Fallon testified before the Senate Armed Services Committee in January, he said, "What we have been doing has not been working. We have got to be doing, it seems to me, something different."

Earlier this week, the Pentagon issued its bleakest assessment of the war to date, saying in a new quarterly report that last October through December was the most violent three-month period since 2003.