[cnn-photo-caption image= http://i2.cdn.turner.com/cnn/2010/images/06/24/art.petraeus.0624p.gi.jpg caption=" Gen. David Petraeus told CNN on Thursday that he supports President Barack Obama's July 2011 deadline to start withdrawing U.S. troops from Afghanistan."]Washington (CNN) - Gen. David Petraeus told CNN on Thursday that he supports President Barack Obama's July 2011 deadline to start withdrawing U.S. troops from Afghanistan, a key point of contention between the president and many of his Republican critics in Congress.
Petraeus - tapped to replace Gen. Stanley McChrystal as the U.S. commander in Afghanistan - also expressed his respect and appreciation for McChrystal's work and said the circumstances surrounding the change in command are "sad."
McChrystal was relieved of duty on Wednesday after he and his staff made comments in a Rolling Stone magazine article that appear to mock top Obama administration officials.
Petraeus's remarks to CNN's Dana Bash and Ted Barrett were his first public comments since being chosen as the new U.S. military chief for the Afghan conflict. The Senate Armed Services Committee is set to begin confirmation hearings for Petraeus next Tuesday morning.
"I support the president's policy, and I will also provide the best professional military advice as we conduct assessments," Petraeus said.
The general said it's a privilege to serve. "It's obviously a hugely important mission," he said.
"It's very sad that I have to assume it in this manner," he added. "We obviously all have enormous respect and gratitude to Gen. McChrystal for all that he did. He's played a key role in helping get the inputs right in Afghanistan."
Petraeus declined to immediately say whether he would fire the unnamed officers on McChrystal's staff quoted by Rolling Stone making disparaging remarks about civilian authorities.
"You have to understand, an officer - a commander - cannot prejudge a situation because that crosses the line into what is called 'command influence,'" he said. "So we'll need to sort out the facts and take the appropriate action once we've done that."
The decision to replace McChrystal with Petraeus was hotly debated by top administration officials. Defense Secretary Robert Gates backed keeping McChrystal on the job because he was vital to the war effort in Afghanistan, but he was overruled, a senior Pentagon official told CNN. The official has direct knowledge of the events but declined to be identified because of the internal administration discussions.
The country's top U.S. military official - Joint Chiefs Chairman Adm. Mike Mullen - said Thursday he backs the president's decision to remove McChrystal from the Afghan command post. "I'm very supportive of the president's decision," he said.
Military officers on the ground in Afghanistan, meanwhile, are stressing Obama's assertion that the switch in leadership does not represent a change in policy.
"We remain absolutely focused on our tasks and the operational tempo will not miss a beat," Lt. Gen. Sir Nick Parker said Thursday. Parker, who is British, has assumed command pending approval of Petraeus' nomination by Congress.
Petraeus, who also led the U.S. military surge in Iraq, expressed gratitude towards his wife Thursday when asked about her feelings on his new assignment
"She's a great wife, army daughter and army mother," he said.
- CNN's Ted Barrett, Dana Bash, Barbara Starr and Alan Silverleib contributed to this story