WASHINGTON (AP) – Secretary of Defense Gates said Friday an effort in Congress to pass a resolution opposing President Bush’s troop buildup undercuts U.S. commanders in Iraq and “emboldens the enemy.”

At the same time, he said the Pentagon is hoping to speed the deployment of five additional Army brigades to Baghdad to bolster security in the capital. They had been scheduled to arrive a brigade per month through May, each containing roughly 3,500 troops.

Mr. Gates’ strong language, along with Mr. Bush’s own forceful comments, underscored the high stakes in a congressional battle expected to start next week over proposals from both parties criticizing the president’s war strategy.

At the White House on Friday, the president challenged lawmakers not to prematurely condemn his buildup, saying, “I’m the decision maker” on troop levels. Vice President Dick Cheney said earlier this week that the buildup would proceed even if a nonbinding resolution supported by some Republicans as well as Democrats wins Senate approval.

Mr. Bush spoke to reporters in the Oval Office after meeting with Mr. Gates and Lt. Gen. David Petraeus. Petraeus won Senate confirmation Friday to replace Gen. George Casey as the top U.S. commander in Iraq.

Stepping up what has become a war of nerves with Iran, the White House also said Mr. Bush had authorized U.S. forces in Iraq to take whatever actions might be necessary to counter Iranian agents who are deemed a threat.

“It makes sense that if somebody’s trying to harm our troops or stop us from achieving our goal or killing innocent citizens in Iraq, that we will stop them,” Mr. Bush said. “It’s an obligation we all have … to protect our folks and achieve our goal.”

With his showdown with Congress drawing near, the president challenged those who favor a legislative rebuke of the troop buildup to put forward an alternative.

“I know there is skepticism and pessimism and that some are condemning a plan before it’s even had a chance to work,” he said. “They have an obligation and a serious responsibility therefore to put up their own plan as to what would work.”

At a private retreat for House Republicans on Maryland’s Eastern Shore, Mr. Bush did not rule out support for a proposal by the chamber’s GOP leaders calling for benchmarks to measure the Iraqi government’s support for the U.S. effort to quell violence. Top House Republicans are trying to balance a show of support for Bush with broad skepticism among GOP lawmakers that his troop increase will work.

Asked about the House resolution, Mr. Bush said he trusts Republican leaders because he knows they want to succeed in Iraq, said a House GOP official who spoke on condition of anonymity because the meeting was not public.

House Republicans are also proposing an advisory committee to report regularly on the progress of Bush’s plan in an effort to measure how well it is – or isn’t – working to quell sectarian violence in Iraq.

Democrats showed little sign of backing down. Emphasizing Congress’ intention to play a major role in Iraq, House Speaker Nancy Pelosi, D-Calif., led a group of lawmakers there, where they met with Iraqi Prime Minister Nouri al-Maliki and senior U.S. commanders.

“American forces should quickly begin to transition from a combat role to one focused on training, counterterrorism, force protection, and controlling Iraq’s borders,” the delegation said in a written statement, espousing a policy embraced by the bipartisan Iraq Study Group but not the administration.

House Majority Leader Steny Hoyer, D-Md., said the House will vote shortly after the Senate on a nonbinding measure “that makes clear that we need a real change in course, that the president’s escalation proposal does not serve our national interests.”

He also pledged more hearings on the war effort, to be followed by legislation that could require changes in administration policy. He said one possibility is to revise the measure that Congress passed in 2002 giving Bush authorization to invade Iraq.

Gates, at his first Pentagon news conference since taking office Dec. 18, was asked whether he thought a formal rebuke of Bush’s plan would offer Iraqi insurgents new hope.

“It’s pretty clear that a resolution that in effect says that the general going out to take command of the arena shouldn’t have the resources he thinks he needs to be successful certainly emboldens the enemy and our adversaries,” Gates replied.

“I think it’s hard to measure that with any precision, but it seems pretty straightforward that any indication of flagging will in the United States gives encouragement to those folks,” Gates said, referring to the anti-government forces in Baghdad.

Senate Democrats are to start debate next week on a resolution opposing Bush’s decision to send an additional 21,500 U.S. forces into battle in Iraq. Senator Reid, the Majority Leader and Democrat of Nevada, said Friday that a quick test vote would probably be taken if Republicans tried to delay or block the resolution.

General Petraeus, who served in command positions in Iraq twice previously, has said he needs all the extra troops to quell raging sectarian violence in Baghdad.

Mr. Gates said Friday that the Pentagon would see if there were ways of speeding up at least some of the brigades.

Mr. Bush said he wanted General Petraeus to head to Baghdad as quickly as possible to implement his new strategy, which includes economic development as well as more troops.

Mr. Gates defended Mr. Bush’s choice of General Casey to be the next Army chief of staff, despite indications that some lawmakers might oppose him because of the poor progress in Iraq under his command.

Mr. Gates seemed to allude to his predecessor, Donald H. Rumsfeld, in saying that the performance of generals like Casey should be evaluated “in the context of the decisions made by (their) civilian superiors.” He added: “The battlefield they faced was shaped by those decisions.” He did not mention Mr. Rumsfeld by name.

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Associated Press writer Laurie Kellman contributed to this report from Cambridge, Md.