WASHINGTON, Oct 4 (Reuters) - President George W. Bush asked Congress on Tuesday to consider giving him powers to use the military to enforce quarantines in case of an avian influenza epidemic. He said the military, and perhaps the National Guard, might be needed to take such a role if the feared H5N1 bird flu virus changes enough to cause widespread human infection. "If we had an outbreak somewhere in the United States, do we not then quarantine that part of the country? And how do you, then, enforce a quarantine?" Bush asked at a news conference. "It's one thing...