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.
Outgoing British Prime Minister Tony Blair also said Friday he was optimistic about Mr. Bush's strategy but called Iraq a tremendous challenge.
"I've picked the plan that I think is most likely to succeed," Mr. Bush said in an.
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 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."
Senate Democrats have set debate on one measure opposing the planned troop increase for early next week. The non-binding resolution passed the Senate Foreign Relations Committee on a near party-line vote earlier this week.
Senate Democratic leader Harry Reid said the vote will take place despite stiff administration lobbying and a filibuster threat from Senate Republicans, CBS News Radio correspondent Bob Fuss reports.
Democrats have readied several resolutions with different wording, and Reid says he is confident they will find a compromise that brings most Republicans on board.
At Gates's first Pentagon news conference since taking office on Dec. 18, he was asked his reaction to the debate in Congress over the effect of such a nonbinding resolution.
"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," he said.
As controversial as it already is, the surge could be even larger than the 21,500 troops currently slated for Iraq, reports CBS News national security correspondent David Martin. Pentagon officials tell CBS News they are planning for the possibility Petraeus will ask for more.
That will also mean more troops beyond the 24,000 already in Afghanistan — where the Taliban is making a surge of its own, Martin reports. With troops buildups now going on in both Iraq and Afghanistan, the Army and Marines will be stretched as never before.
Speaking from the World Economic Forum in Davos, Switzerland, Blair offered strong support for Mr. Bush's new plan and said he believes the Iraqi prime minister can meet the benchmarks the United States has set.
He said of Iraqi Prime Minister Nouri al-Maliki: "He's a man with the intent, and we've got to support him in having the capacity. That's what it's all about."
Many in Congress have accused al-Maliki of foot-dragging and have challenged his capability to quell the sectarian violence tearing apart his country.
House Speaker Nancy Pelosi and anti-war Democrat Rep. Jack Murtha met with al-Maliki in Baghdad on Friday.
"We come out of the meeting with a greater understanding of the others' point of view," Pelosi, D-Calif., said in brief remarks after the session.
Murtha, D-Pa., who chairs the Appropriations subcommittee for defense, will have a big say in future spending decisions on Iraq. A onetime hawk on military issues, Murtha for more than a year has been one the most outspoken war critics.
A key piece of Mr. Bush's new Iraq strategy is increasing reconstruction efforts, with the U.S. pledging an additional $1.2 billion. Also, Bush is expected to send Congress next month a Pentagon request for about $100 billion more for Iraq and Afghanistan.
While Congress has constitutional purse strings control over war spending, most lawmakers seem hesitant to support a cutoff of funds that might endanger troops now in Iraq.
Gates said there was "no blank check" to U.S. commanders in Iraq to receive an unlimited number of extra troops; instead, they submit requests for what they believe they need and those are reviewed closely by senior officials in the Pentagon, with final decisions left to Mr. Bush.
"What we have done, I hope, is created an environment in which the commanders feel open to requesting what they think they need and then we will evaluate it here in the department to see what's available and how much of that request we can satisfy," he said.
Asked about indications of potential opposition in the Senate to confirming Gen. George Casey as the next Army chief of staff, given the unsatisfactory progress in Iraq under his command, Gates said Casey was the professional military's first choice to succeed Gen. Peter Schoomaker as the chief of staff at Army headquarters in the Pentagon. Casey had been the vice chief of staff before Bush sent him to Baghdad in July 2004.
"I think he's eminently qualified," to head the Army, Gates said.