Mon Sep 9, 7:22 PM ET

WASHINGTON (Reuters) - The U.S. military began deploying anti-aircraft missiles at the Pentagon ( news - web sites) and bases around Washington on Monday for an exercise to test a multi-layered defense of the national capital region, defense officials said.

"Avenger" anti-aircraft systems -- heat-seeking Stinger missiles on wheeled Humvee military jeeps -- will be stationed at the bases for at least four days beginning on Tuesday, including Wednesday's anniversary of Sept. 11 hijack airliner attacks on America.

The officials, who asked not to be identified, told Reuters the "Clear Skies 2" exercise did not call for missiles to carry live warheads. The exercise, similar to one held in the summer, will test the integration of F-16 fighter jets protecting Washington with missiles, radar and emergency communications between the military and civilian agencies.

The military began deploying some of the missile-carrying vehicles around the Pentagon and other bases on Monday and one defense official said Defense Secretary Donald Rumsfeld could order live missiles moved from stand-by to full alert on the launchers.

Washington Air Defense Tightened

By THE NEW YORK TIMES

ASHINGTON, Sept. 10 — A triple layer of air defenses has been laid over the nation's capital in advance of the Sept. 11 anniversary, with high-altitude radar planes scanning the skies, high-performance jet fighters flying 24-hour patrols and surface-to-air missiles being loaded into launchers late tonight.

On orders of Defense Secretary Donald H. Rumsfeld, the Avenger missile system was loaded with heat-seeking Stinger missiles, which are designed to defend against low-altitude airplanes even if they are traveling at high speeds. The system, which includes eight Stingers in two reloadable pods, is carried atop a Humvee troop transport vehicle.

The Stinger can also defend against helicopters, but not other missiles. Some handheld Stingers were also readied for use.

Though small numbers of surface-to-air missiles have been posted at certain government buildings over the years, military officials said this was the first deployment of surface-to-air missiles widely across the Washington region since 1961, during the Cuban missile crisis.

Air Force F-16's have been deployed in 24-hour patrols over Washington and New York since Friday. Other attack jets and support aircraft across the country remain available on "strip alert," which means they can be airborne at short notice.

The nation's premier airborne surveillance and command jet, the E3 Awacs, is also on 24-hour patrol over Washington. The distinctive black-and-white, mushroom-shaped radar dome atop the modified Boeing 707 has a range of 250 miles and can monitor movement from the surface of the earth up to the stratosphere, officials say.