WASHINGTON -- The Bush administration warned Iraq on Friday that it will have "zero tolerance" for any attempts to thwart U.N. weapons inspections, as the Pentagon prepared for fresh troop call-ups and a possible invasion to topple Saddam Hussein.

The Pentagon, quietly gearing up for war, already has tens of thousands of troops in the region as well as hundreds of planes and other military equipment. Two aircraft carrier battle groups are within striking distance of Iraq, and two more are heading to the region.

Defense Secretary Donald H. Rumsfeld said late Friday that the United States would "keep the pressure up" on Iraq and continue its war preparations and its air patrols of the northern and southern no-fly zones over Iraq.

"The minute that Saddam Hussein and his small ruling clique sense that they're out of danger, I suspect that they'll have no further incentive to cooperate, and any U.N. inspection and disarmament efforts could then fail," Rumsfeld said at a rare evening news conference at the Pentagon with German Defense Minister Peter Struck.

Rumsfeld also suggested -- without saying so outright -- that further Iraqi firing on the U.S. air patrols might be considered a violation of the latest U.N. resolution.

"Iraq ought not to take or threaten hostile action against inspectors or coalition aircraft upholding U.N. inspections," Rumsfeld said. But he later refused to say if he meant that statement as a warning to Iraq not to fire on the no-fly-zone patrols. He said plans for any help by U.S. military aircraft to the U.N. inspection teams had not been worked out.

About 58,000 National Guard and reserve soldiers are now on active duty for the war on terrorism. Thousands more would be needed for an attack on Iraq, possibly as many as the some 250,000 activated for the 1991 Persian Gulf War. Rumsfeld said this week that new call-ups for an Iraq campaign could come at any time.

Seeking domestic backing for any war effort, Deputy Defense Secretary Paul Wolfowitz gave awards Friday to five companies for their support of employees in the reserves. Call-ups can last from weeks to one year with a second year extension possible.