"Ultimately, the decision has been made," he said. "With a decision made, obviously I support that, and will do all that I can during my remaining time as the commander of ISAF [International Security Assistance Force] to implement it, to set up Gen. [John] Allen to do likewise, so we can achieve the objectives of the campaign plan."
Petraeus was appearing before the Senate Intelligence Committee for his confirmation hearing to become head of the Central Intelligence Agency. Lt. Gen. John Allen was tapped as Petraeus' replacement in Afghanistan.
The president told the nation in a prime time address on Wednesday that 10,000 U.S. troops will be leaving the war by the end of 2011, with another 23,000 coming out by autumn of 2012. The drawdown will fully remove the troops that went in as part of the "surge" that Obama announced in his 2009 speech at West Point. Approximately 68,000 troops will still be fighting in the war.
Obama met with his national security team in a series of three meetings, according to Petraeus. At the first meeting, the president asked Petraeus for his recommendations about the drawdown. By the third meeting, Obama had made a decision.
On Thursday, Joint Chiefs of Staff Chairman Adm. Michael Mullen told the House Armed Services Committee that he accepted and supported Obama's strategy, although it was "more aggressive and [will] incur more risk than I was originally prepared to accept."
Petraeus made similar comments before the Senate committee, but made clear that he also supported and would carry out the president's recommendations.
"The commander in chief has decided, and it is then the responsibility -- needless to say -- of those in uniform to salute smartly and to do everything humanly possible to execute it," he said.
He added that the president had "broader considerations beyond just those of a military commander" when making a decision and ultimately, "there's never been a military commander in history who has had all the forces he would like to have for all the time, with all the money, all the authorities and, nowadays, with all the bandwidth as well."
On Wednesday before Obama's speech, both House Speaker John Boehner (R-Ohio) and Senate Minority Leader Mitch McConnell (R-Ky.) said they would accept the president's new strategy as long as it had the backing of military leaders.
Two administration officials told The New York Times that Petraeus did not sign off on Obama's decision, and it was a "setback" for the general.
But in a press call on Wednesday, a senior administration official told reporters that Obama drew his recommendations from what Petraeus put forward.
"Gen. Petraeus presented the president with a range of options for pursuing this drawdown," said the official. "There were certainly options that went beyond what the president settled on in terms of the length of time that it would take to recover the surge and the pace that troops would come out -- so there were options that would have kept troops in Afghanistan longer at a higher number. That said, the president's decision was fully within the range of options that were presented to him and has the full support of his national security team."