WASHINGTON -- Iraq could try to jam U.S. military satellite signals during a possible invasion, but the United States has defenses against such attempts, Pentagon officials said Wednesday.

Indonesia reportedly jammed signals from a commercial satellite leased by the Pacific nation of Tonga in 1997, and Iraq could try to do the same thing, said the Air Force's space operations director, Maj. Gen. Franklin Blaisdell. Iraq also reportedly is seeking ways to jam the Global Positioning Satellite signals that help guide U.S. bombs.

"Any enemy that would depend on GPS jammers for their livelihood is in grave trouble," Blaisdell said at a Pentagon news conference.

Also Wednesday, Gen. Tommy Franks, who would run the war in Iraq, arrived at the military's command center in Qatar. It was not known whether he would return to the United States, visit other nations in the Persian Gulf region, or stay in Qatar to position himself for the start of military action.

Army Chief of Staff Gen. Eric Shinseki, testifying before a House Appropriations subcommittee, repeated his view that the number of troops needed to occupy a postwar Iraq could be several hundred thousand. When Shinseki first made that estimate last month, Defense Secretary Donald H. Rumsfeld and Deputy Defense Secretary Paul Wolfowitz said the estimate was far too high.

Speaking to reporters later, Shinseki called it "sort of a rough estimate," saying that a more accurate estimate could be given by Gen. Tommy Franks, the U.S. commander in the region.

U.S. aircraft dropped 120,000 leaflets over several sites between Baghdad and the southern city of Basra. The messages included a warning to the Iraqi military not to use chemical or biological weapons against U.S. or allied troops, according to U.S. Central Command.

The Air Force canceled a combat training exercise scheduled this month at Nellis Air Force Base, Nev., citing the likelihood of war soon in Iraq.

The Army has more than 1,000 transmitters that help it keep track of soldiers and units while a battle is going on, Fox said. Soldiers can carry the transmitters in their packs or on their belts, and equipment such as helicopters or tanks can have the transmitters attached, Fox said.

As it did during the 1991 Persian Gulf War, the Defense Department is buying access to commercial communications satellites to help serve the massive bandwidth needed to connect all the high-tech gear, Blaisdell said. The military also successfully launched a broadband communications satellite on Monday, he said.