Obama: U.S. Will 'Not Miss a Beat' in Afghanistan As Gen. David Petraeus Takes Over

President Obama and administration officials today expressed confidence about the direction of the U.S. strategy in Afghanistan as the new mission's new commander, Gen. David Petraeus, prepared to head to the region next week.

"What we saw yesterday was a change in personnel not a change in policy," the president said at a joint news conference with Russian President Dmitry Medvedev. "We will not a miss a beat because of the change in command in the Afghan theater."

VIDEO: Obama on Command Change: We Will Not Miss a BeatPlay

Petraeus' confirmation hearing will be held next Tuesday, and while the general -- widely praised by both Republicans and Democrats -- is unlikely to face any hurdles, the hearing will likely resurrect the debate over whether the United States should start pulling out its troops in Afghanistan by next year.

The president reiterated today that a review will be completed by December to gauge U.S. progress in Afghanistan and a decision about future U.S. strategy will be made accordingly.

VIDEO of Gates and Mullen Weighing in on Change of CommandPlay

The issues that led to Gen. Stanley McChrystal being relieved Wednesday "were not as a result of a difference in policy," Obama said. McChrystal resigned after disparaging comments he and his aides made in a Rolling Stones article raised uproar in Washington and led many to question the relationship and trust between the civilian and military leaders on the grouns.

The change in U.S. command comes amidst the backdrop of the deadliest month in Afghanistan for NATO. Seventy-nine NATO troops died this month in the country, higher than the previous record of 77 deaths last August. June is also likely to be one of the deadliest months for U.S. troops, with 44 Americans killed so far this month.

VIDEO: Sen. John McCain, R-Az., weighs in on whether a new war strategy is needed.Play
Sen. John McCain on Obama's Change of Command

Gates admitted today the war in Afghanistan is "slower and harder than anticipated," but he added that the United States is "making progress" and he doesn't feel it is "bogged down."

Chairman of the Joint Chiefs of Staff Adm. Mike Mullen will head to the region today to deliver that message.

"My message will be clear. Nothing changes about our strategy, nothing changes about our mission," Mullen said today.

Meanwhile, the fate of many of McChrystal's aides quoted in the article by Michael Hastings is unknown. Col. Charlie Flynn, McChrystal's chief of staff, will not be returning to Afghanistan. Duncan Boothby, a civilian press official in Afghanistan, resigned immediately in the aftermath of the scandal, but the job prospects of others are unclear.

Both Gates and Mullen today denounced McChrystal's comments as irresponsible and concurred that he was rightfully held accountable for comments made by him and his aides belittling administration officials.

"I cannot excuse his lack of judgment with respect to the Rolling Stone article or a command climate he evidently permitted that was at best disrespectful of civilian authority," Mullen said, adding that those in uniform do "not have the right, nor should we ever assume the prerogative to cast doubt upon the ability or mock the motives of our civilian leaders, elected or appointed."

Mullen said when he first read the story, he was "nearly sick, literally, physically. I couldn't believe it."

Petraeus' successor, the new head of the United States Central Command, has yet to be announced.

U.S. Afghanistan Strategy Questioned

A day after Obama replaced McChrystal with Petraeus, Sen. John McCain, R-Ariz., urged the president not to stop there and questioned his timeline.

"It's completely understandable why the president made the decision that he did, based on the civilian-military relationship that goes a long way back," McCain said today on "Good Morning America." "I also point out to the president, with my strong support of Petraeus, we also need a new team over there as well -- perhaps at the embassy and other areas."

"I pointed out to the president that if he insists on a date-certain [withdrawal], rather than a conditions-based [withdrawal]... then we cannot succeed," McCain added.

McChrystal was recalled from Afghanistan for a Wednesday meeting with Obama after Rolling Stone printed an profile of the general in which he and his top aides made disparaging remarks about several top U.S. officials.

The profile published in Rolling Stone, titled "The Runaway General," characterized McChrystal as an outsider who did not relate well with the administration, and as a military leader who was "disappointed" with his first meeting with the president.

It highlighted the often tense relationship between the civilian and military arms of the U.S. command in Afghanistan, and included many disparaging comments about top U.S. officials, mostly made by McChrystal's aides.

In quick succession, the president met with McChrystal in the White House Wednesday, accepted his resignation, met with Petraeus just minutes later and asked him to take over the job.

McChrystal's conduct, as detailed in the Rolling Stone article, "does not meet the standard that should be set by a commanding general," the president said Wednesday. "It undermines the civilian control of the military that is at the core of our Democratic system, and it erodes the trust that's necessary for our team to work together to achieve our objectives in Afghanistan."

The president praised McChrystal for his "extraordinary dedication" and "love of the country," but made it clear the comments McChrystal and his aides made could jeopardize the U.S. mission in Afghanistan.

The decision to elect Petraeus for the position came from the president himself, Gates said today.

The 57-year-old commander is jokingly referred to by some in the military as a "water walker" with a near legendary ability to turn even the worst situations around.

He received enormous credit by many for turning the corner in Iraq where he served three different tours, the last overseeing the surge, but was also criticized heavily for his strategy.

It will be the second time Petraeus has replaced an officer whose career was sidetracked by a magazine profile. In 2008. Adm. William Fallon lost his job at Central Command after an Esquire article put him at odds with the Bush administration.

On the ground, news of McChrystal's dismissal and Petraeus' new position was met with surprise, but also a sense of relief that an experienced commander will take the helm.

As one Marine told ABC News, "the softball is teed up for Petraeus to hit it out of the park."

The war in Afghanistan has become the longest war in U.S. history, and more than 1,000 troops have died there since the U.S. invaded the country in 2001.

ABC News' Miguel Marquez and Nick Schifrin contributed to this report.