Less than 40 miles from the border with Iraq, this desert air base provides the U.S. military with the closest permanent installation from which invasion forces could be launched.

That proximity makes at least some of the 1,500 American troops here nervous.

"When you get this close to the border, it can be scary," said Senior Airman James Mack, a guard who puts in 14-hour workdays scanning the base's perimeter for intruders. "The best thing is not to think about it."

But when they do, soldiers here say they worry most about the prospect of Iraq unleashing chemical or biological agents. While the Pentagon has been warning Iraq against resorting to weapons of mass destruction, U.S, intelligence officials suspect that President Saddam Hussein may issue orders to use them in a final act of desperation. And if he does, this base could be a likely target.

To guard against such a possibility, the Pentagon has positioned Patriot missile interceptors in the vicinity for blasting Iraqi warheads out of the sky, and soldiers run regular drills to ensure they could don protective masks within seconds.

But there are obvious advantages to being this near the front, and the Pentagon has stationed some key assets here, including unmanned Predator aircraft that are regularly sent over Iraq on reconnaissance missions and Army RC-12 electronic intelligence-gathering aircraft.

The Army also is using the base to position its lead attack weapon, the Apache helicopter, as far forward as possible and still have the benefit of hangars and other permanent facilities. A squadron of 21 Apaches, armed with Hellfire missiles and 30mm cannons, arrived here from Germany in October.

Maj. Carl Coffman Jr., the squadron's executive officer, is hoping that if war comes, the Apaches will be chosen to deliver the first strikes. Apaches fired the initial shots in the 1991 Persian Gulf War against Iraq, knocking out radar facilities that helped blind Iraq's air defense system to the first waves of U.S. bombing.

Since its arrival, the squadron, which belongs to the 11th Aviation Regiment, has been practicing potential invasion scenarios with a brigade of more than 4,000 infantry troops, members of the 3rd Infantry Division. At least one more brigade is expected to start arriving next month as the Pentagon intensifies a buildup of forces in the region.

Including support personnel and the senior command staff that would be responsible for overseeing land operations in an invasion, the Army has more than 10,000 troops in Kuwait, and the Air Force has several thousand more, evidence of Kuwait's central importance in U.S. war plans.

Gen. Richard Myers, chairman of the Joint Chiefs of Staff, toured the land forces command center today at Camp Doha near Kuwait City and expressed approval of progress there in establishing the communications and intelligence-collection links that would be vital in monitoring operations during a war.

At the camp, which occupies a port facility, Myers also caught a glimpse of the massive amount of combat equipment that has flowed into Kuwait in recent weeks, enough for thousands of additional troops.

But the buildup, while already substantial, remains far from reaching any point of no return, Myers said. Completing a three-day tour of Kuwait, Qatar and Afghanistan, Myers said an invasion of Iraq was not inevitable.

"From a military standpoint, we're flexible," he said in an interview. "We can build up, we can build down. The only folks who can determine if we reach a point of no return is the Iraqi regime."