WASHINGTON - President Obama, in an interview being broadcast tomorrow, defended his decision to set a deadline to begin withdrawing U.S. forces from Afghanistan.

"In the absence of a deadline, the message we are sending to the Afghans is: 'It's business as usual. This is an open-ended commitment' " by the United States, Obama told CBS's 60 Minutes. "That's not what the American people signed up for when they went into Afghanistan in 2001."

The network released an excerpt from the interview.

Obama announced Dec. 1 that he would deploy 30,000 more U.S. military personnel to Afghanistan by mid-2010. In addition, Afghan forces are to begin taking over responsibility for security as the extra U.S. forces begin pulling out starting in July 2011, he said.

"There are, I think, elements in Afghanistan who would be perfectly satisfied to make Afghanistan a permanent protectorate of the United States," Obama said in the interview, recorded earlier this week.

That would put the full burden on the United States for providing Afghanistan's security, he said. The U.S. public, Obama said, supported waging the war "to go after al-Qaeda."