TAMPA, Fla. (AP) - Any effort to legislate a deadline for U.S. withdrawal from Iraq will "make it difficult if not impossible" for military commanders to do their mission, Defense Secretary Robert Gates said Friday. Both the Pentagon and the Iraqi government have gotten the message that Congress is losing patience with the war, said Gates, speaking to reporters as he flew back to Washington from a ceremony installing the new U.S. commander for the Middle East. It's clear, he said, "that there's a great deal of impatience to see progress. Congress doesn't want to see an open-ended conflict," Gates said, "If the intention was to send a message, that message has been received - not just by us ...but by the Iraqis." Gates flew to Tampa for a change-of-command ceremony where Navy Adm. William Fallon was installed as the new head of U.S. Central Command. In remarks at the ceremony, Gates said 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. The United States is "dedicated to strengthening those commitments and defending our interests for decades to come. And we will do all in our power to protect and defend our homeland," said Gates. He spoke before 600 top military commanders, guests and rank-and-file servicemen and women crowded into the airport hanger at MacDill Air Force Base for Fallon's installation ceremony. Fallon, whose new assignment puts him in charge of American forces in the Middle East and Central Asia, told the crowd that, "The situation in Iraq is critical and time is of the essence." Fallon replaced Gen. John Abizaid, who led Central Command since 2003 but is leaving as part of a reshuffle of Mideast military commanders by President Bush. Besides Iraq, Fallon will also oversee the war in Afghanistan, where Gates is pushing for a coalition offensive to counter the expected increase in Taliban attacks as the weather warms this spring. The U.S. has already increased forces there. "I am sure that General Abizaid would agree that not everything has gone as planned, as expected, or as hoped," Gates said. "This is the nature of war." He said that Abizaid realized early on that the fight against jihadist extremism "would be a long and difficult endeavor." Abizaid repeated a warning he has proffered often during his command - that the U.S. is fighting an evil ideology in a long war that is much bigger than just Iraq and Afghanistan. "War is never easy, nor pretty, nor easily resolved," said Abizaid. "We will need both courage and time to withstand the impatience and dissatisfaction that could cause us to fail despite our great abilities to succeed." 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. Speaking directly to Fallon, Gates said: "We need you again. You are one of the best strategic thinkers in uniform today. You are exactly the right person for this post." "Much work is in front of us," Fallon said in brief remarks after accepting the flag of command from Abizaid in a rainy-day ceremony steeped in military symbolism. The change in command 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. 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. --- On the Net: Defense Department: www.defenselink.mil © Copyright 2007 Associated Press. All rights reserved. This material may not be published, broadcast, rewritten, or redistributed.