WASHINGTON - The top commander of U.S. forces in Afghanistan, Gen. Stanley McChrystal, has said that setting a withdrawal date forces Afghan leaders to take their own security seriously. In an extended interview being broadcast Sunday on CNN, McChrystal said the date lets Afghans know the United States "cannot have an endless surge of a significant number of combat forces." "It's a forcing function to make people step up," he added. McChrystal said the July 2011 date set by President Barack Obama is not premature and that western forces in Afghanistan do not need more time "to get this moving in a direction where the Afghans have confidence." Obama announced last week the deployment of another 30,000 U.S. forces to Afghanistan, increasing the total U.S. troop commitment to almost 100,000, while at least 25 other countries have pledged another 7,000 troops. But McChrystal said Obama's additional goal to begin withdrawing U.S. troops in July 2011 will force Afghan officials to take the lead on ensuring their country's security. "[The withdrawal date] tells people that we cannot have an endless surge of a significant number of combat forces," he said. "It's a forcing function to make people step up." Afghan President Hamid Karzai has said his forces will take the security lead in five years, despite doubts among military analysts that the Afghan army and police will be able to provide a sufficient number of trained forces in that period. McChrystal rejected concerns that the July 2011 withdrawal is too early. "It will take longer, but it won't take longer to turn the momentum," he said. "It won't take longer to get this moving in the direction where Afghans have confidence." McChrystal said he has already seen counterinsurgency efforts reverse the momentum of the Taliban in such areas as central Helmand and parts of Kunar and Khost provinces. With the troop surge starting early next year, McChrystal said the strategy will be "to take away from [insurgents] that which they need -- access to the population. It's to go to key areas, expand security in those areas, and prevent the insurgents from having access." McChrystal said the goal is to protect population centers to enable the government to improve security and governance. He also stressed the importance of avoiding civilian casualties, which have drawn criticism from Afghans, because they make it less likely the Afghan people will support the coalition. "It is better to miss a target than to cause civilian casualties," he said. "We can always target enemy leaders later. We can't make up for the fact that we killed civilians."