A steep jump in missions at home and abroad since last year's terrorist attacks in New York and Washington has Air Force crews working harder but losing some of their edge, according to Air Force officials.

Because of more frequent deployments and extended tours in Afghanistan and elsewhere, many aircrews have had less time to practice a full range of combat skills, and Air Force authorities report greater difficulty retaining experienced personnel. A falloff in training also has resulted in a rise in the number of inexperienced personnel filling positions, officials said.

These problems, while far from being across the board, are nonetheless worrisome to Air Force officials, who point to a drop this year in what they call "unit readiness" -- a composite measure of training, retention and maintenance rates -- to its lowest level in more than a decade. The trend also is of concern to commanders planning for a possible invasion of Iraq.

With United Nations inspectors having begun their hunt for weapons of mass destruction in Iraq, U.S. military authorities are pondering how to keep forces ready for a potential attack without exhausting them. It is a tricky calculation that involves such decisions as how many troops to keep in Afghanistan, how fast to build up forces in the Persian Gulf area and whether to reduce operations elsewhere.

"No question that once you get a military force at a peak level of preparedness, it starts to deteriorate in all kinds of ways," a high-ranking defense official said.

While all military branches have felt the strain of the Bush administration's global war on terrorism, the Air Force has been especially stretched by the combination of combat air patrols over U.S. cities, a war in Afghanistan and continued enforcement of "no-fly" zones over northern and southern Iraq. The number of Air Force personnel deployed to the Persian Gulf region has increased more than threefold this year, from 5,500 to more than 18,000.

In interviews about the stresses on aircrews, several senior Air Force officials spoke of tensions, particularly with the U.S. Central Command, which oversees military operations in the Middle East, over which forces were being called and how many were being assigned to operations in Afghanistan, the Gulf and the Horn of Africa.

"We're not whining about having to do this; we're simply pointing out that there's a cost to it," one Air Force general said.

In the Air Force, the AWACS monitoring plane is emblematic of how the service is coping under the strain. Topped with a rotating radar dome and crammed with computers and communication gear that enable operators to track planes and manage air battles, the AWACS, or Airborne Warning and Control System, is critical to any Air Force combat mission.

Because the fleet of 33 AWACS is well short of the number often in demand, the plane falls in a category of weapons systems that the Pentagon calls "high demand, low density." This includes such other specialty aircraft as RC-135 Rivet Joint electronic warfare planes, JSTARS ground surveillance aircraft, U-2 high-altitude reconnaissance planes, EA-6B Prowler jammers and Special Forces planes.

"It's great to be loved, but it has a downside," said Brig. Gen. Mike Hostage, commander of the 552nd Air Control Wing at Tinker Air Force Base in Oklahoma City, home for most of the nation's AWACS aircraft.

Even before Sept. 11, 2001, AWACS planes were kept busy flying patrols over northern and southern Iraq and counterdrug operations over the Caribbean and South America. The counterdrug flights were stopped as AWACS planes a year ago joined combat air patrols over U.S. cities and the war in Afghanistan. Even so, the 552nd wing flew more than 23,000 hours in the 12 months after Sept. 11, well in excess of the 16,000 hours planned for the year. AWACS crew members continue to average about 180 to 200 deployment days a year, far above the Air Force's desired maximum of 120 days.

Because of the increase in deployments, authorities at Tinker have lacked planes and instructors for training. The wing has accomplished only 30 percent its planned refresher training for existing crews and 75 percent of its planned qualifying flights for new crews. The number of crew members failing to meet annual training requirements has increased tenfold over the past year, officials said.

In some instances, the turnaround time for crews' completing a tour has been too short to allow for much rest. "Some of our guys are coming back home and, 30 days later, they're back in either a 45-day or 90-day deployment," said Maj. Anthony Shaw, a mission commander with 71/2 years of experience flying AWACS planes.

The long hours and time away from home also have contributed to the exodus of key personnel, especially radar technicians. The 552nd wing lost 30 percent of its technicians over the summer after a "stop loss" policy barring personnel from leaving the service was lifted.

To retrieve the handful of AWACS aircraft still in use over Afghanistan, Air Force officials have pressed the Central Command to consider employing such alternatives as Navy P-3 patrol planes, carrier-based E-2 Hawkeye early warning aircraft, or AWACS planes owned by Britain and NATO. NATO's contribution of six AWACS planes last autumn for air patrols over the United States saved the wing at Tinker from halting training altogether, officials said.

Also under consideration for Afghanistan is the installation of additional ground radars, operated either by Americans or Afghans.