Enlarge By Justin Sullivan, Getty Images U.S. Army soldiers carry a critically wounded colleague on a stretcher Thursday to a waiting helicopter near Kandahar, Afghanistan. WASHINGTON  Defense Secretary Robert Gates said Thursday that the United States and its allies are not "bogged down" in Afghanistan despite the delay of a planned offensive in the southern city of Kandahar . The remarks come one day after President Obama relieved the commander of allied forces in Afghanistan, Gen. Stanley McChrystal, and nominated Gen. David Petraeus to replace him. U.S. officials worked to allay concerns that the abrupt change reflects any lack of commitment on the part of the White House or flaws in its strategy. Obama said the United States will "not miss a beat" as a result of the change. HEARTS AND MINDS: Negotiation is Army's secret weapon One of the key advantages of appointing Petraeus is his familiarity with the region, Gates said. Petraeus heads Central Command, which oversees wars in Iraq and Afghanistan, and so will need little schooling before assuming command. The Defense secretary said Obama himself raised the idea of replacing McChrystal with Petraeus during a meeting Tuesday. Key Senate leaders pledged to quickly confirm Petraeus' appointment in order to minimize any disruption caused by the change. Sen. Carl Levin, D-Mich., chairman of the Armed Services Committee, announced a Tuesday morning hearing. Obama accepted McChrystal's resignation after the general and his top aides were quoted in a Rolling Stone article describing their civilian leaders or counterparts in disparaging ways. Adm. Michael Mullen, chairman of the Joint Chiefs of Staff, and Gates praised McChrystal's career but did not defend or excuse the remarks in the article. "Honestly, when I first read it, I was nearly sick," Mullen said. "I was stunned." Mullen said the comments from McChrystal and his staff had the effect of challenging civilian oversight over the military, a bedrock principle. Nevertheless, Gates and Mullen drew a distinction between the intemperate remarks made by McChrystal and his staff and the conduct of the war. The leadership change comes at a critical time. About 30,000 additional servicemembers have been pouring into Afghanistan as part of a broader effort to seize the initiative from the Taliban. An offensive in Marjah, a Taliban stronghold in the south, decisively drove insurgents from the town this winter, but the U.S. military and Afghan government have struggled to build an effective local government in its wake. Coalition and Afghan forces are now turning their attention to Kandahar, which was the Taliban's spiritual homeland. Gates said the military needed more time to improve political conditions there before starting the offensive. "I do not believe we are bogged down," Gates said. "I believe we are making some progress. It is slower and harder than we anticipated." Guidelines: You share in the USA TODAY community, so please keep your comments smart and civil. Don't attack other readers personally, and keep your language decent. Use the "Report Abuse" button to make a difference. You share in the USA TODAY community, so please keep your comments smart and civil. Don't attack other readers personally, and keep your language decent. Use the "Report Abuse" button to make a difference. Read more