WASHINGTON -- As North Korea makes increasingly loud threats of war, nearly half the Air Force's workhorse C-141 transports, used for ferrying troops and equipment to any conflict, are grounded for maintenance.

The erosion of the military's aging airlift capacity -- crucial to U.S. engagement in the regional conflicts that plague the post-Cold War world -- is heightening concern inside and outside the Pentagon.

"Airlift in this country is broken right now," Gen. Joseph Hoar, commander in chief of the U.S. Central Command, told the Senate Armed Services Committee this month.

General Hoar said that airlift problems would prevent the U.S. military from fighting the two almost simultaneous regional conflicts that it should be able to handle under current guidelines. Defense planners believe that one such conflict could be in Korea.

Tension on the peninsula has been heightened by confrontation over North Korea's refusal to allow inspection of its nuclear facilities. While U.S. officials stress that there is no sign of any imminent attack from the North, the government in Pyongyang warned Thursday that imposition of United Nations economic sanctions, under consideration to force North Korean compliance, would be viewed as a declaration of war.

"If a conflict were to break out [in Korea], we would need a much larger number of forces and materiel to move into that theater, and it might be needed there very quickly," said Loren B. Thompson, deputy director of Georgetown University's National Security Studies Program. "It is widely recognized that the U.S. at present does not possess the airlift required in order to quickly respond to a range of potential regional conflicts."

Noting that 90 percent of U.S. equipment in previous U.S. foreign conflicts has been delivered by sea, he said, "Airlift is not crucial except during the early stages of a war, when rapid response vTC may have a decisive effect on the future progress of the war."

Airlift fleet 'marginal'

The Air Mobility Command, which operates the airlift, has assessed the health of its Lockheed C-141 Starlifter fleet as "marginal," although a command spokesman said, "We are fully capable of meeting crisis contingency operations."

To meet current transport demands, the command, based at Scott Air Force Base, Ill., has converted Boeing KC-135 and McDonnell-Douglas KC-10 refueling tankers into cargo carriers and leases planes from 14 civilian airlines.

Its C-5 Galaxies, which can airlift three times as much as the C-141s, are also being pressed into extra service, but there is a limit to how much more they can do. Maj. Jereon Brown, the command spokesman, said the C-141 repair schedule was "not hampering us to a sizable extent" but was causing "minor delays" to low-priority movements.

Of the Air Force's 244 C-141s, 105, or 43 percent, are undergoing maintenance. The plane reached its operational low point in November, when 173 were grounded for repairs to correct a wing fault.

In the event of conflict, Major Brown said, planes under repair that were flyable would be "pulled" out of maintenance and "sent to war or wherever they needed to go."

Sen. Ted Stevens, a member of the Senate Appropriations Committee's defense subcommittee, said in an interview last week, "We have got an aging fleet of C-141s, and they are showing the signs of age."

The senator, who expressed his concerns to Defense Secretary William J. Perry at a congressional hearing this month, told The Sun, "I would not want to imply in any way we are not capable of meeting any crisis that comes along.

"The difficulty is that each crisis takes a bigger bite out of the life cycle of the airlift and accelerates the time when there has to be ready a suitable [airlift] replacement for next-century utilization," said.

Testifying before the House Armed Services Committee last week, the deputy undersecretary of defense, Walter B. Slocombe, said: "The ability to deal with aggression in Korea is one of the measuring factors in our defense planning. Together with our South Korean allies, we have made extensive preparation to deter and, if necessary, to defeat a North Korean attack."

Timetable for war

The Pentagon's guidelines set a timetable for U.S. airlift and sealift capacity that would be needed to fight a war in Korea:

* Immediately: Field a three-brigade heavy Army division with support units, seven to eight fighter wings and two Marine brigades.

* Within a month: Deploy the remainder of a three-division Army heavy corps, the remainder of 10 Air Force fighter wings and additional Marine forces.

* Within six weeks: Assemble a force strong enough to launch a successful counterattack.

The United States has a considerable military presence in and around Korea. Some 37,000 U.S troops are stationed in South Korea to defend against an attack by North Korea's army of more than 1 million troops. About 15,000 troops from the U.S. 2nd Infantry Division and the 17th Aviation Brigade are deployed near the Demilitarized Zone between the two Koreas. An additional 8,500 are attached to the 8th and 51st Tactical Fighter Wings, with 72 F-16 fighters.

About 46,000 U.S. troops are based in Japan. A 45,000-troop Marine Expeditionary Force is attached to the U.S. 7th Fleet, which patrols the Western Pacific. More Marines are based on Guam.

Such a U.S. war machine, if activated, would be supplied by sea as well as air, and materiel is positioned, on land and in ships, in the Western Pacific, Europe and the Middle East, where conflicts could occur. This reduces the airlift burden, but does not diminish its role.

During the Persian Gulf war, for example, the airlift carried 500,720 troops, or 99.45 percent of the personnel, and 543,548 tons of equipment, or 14.78 percent of all non-petroleum cargo. The C-141s carried 19 percent of the passengers and 1.6 percent of the cargo.

Patriot anti-missile missiles are being sent to South Korea by sea this month because, said Mr. Perry, "There might be a confrontation point or a crisis point later in the year, and if and when that happened . . . in an emergency, if we had to move those over by air, they would consume 80 or 90 C-5s [transports]."

Mr. Perry said: "They really take up an enormous amount of airlift at a time when we would want to be using it for other purposes."

The C-141s, introduced in the mid-1960s, are, according to a Defense Department report to the president and Congress, "nearing the end of their projected service life."

The planes have developed wing problems, and the entire fleet is being overhauled to try to keep the planes flying until they can be replaced, which, according to the Pentagon's annual report, "remains an urgent requirement."