They call it "rat-racing" - high G-turns that crunch the pilots down in their seats, blasts of afterburner acceleration, simulated missile firings, electronic games of tag staged in the skies five miles up over South Korea.

The warplanes with the U.S. markings are always pursuing make-believe Migs, theoretically in the hands of North Korean fliers.

One of the "rat-racers," U.S. Air Force Capt. Charlie Sylling, flew his camouflaged F-4 Phantom jet into Osan Air Base at 180 knots after a recent training sortie and released the brake chute.

"Obviously we are not training against some other folk, we're training against the North Koreans," he said. "Our state of readiness is high . . . In planes and people we can go to war tomorrow if we have to."

Charlie Sylling and the other 8,300 U.S. Air Force personnel in South Korea are not going home. As U.S. ground troops are pulled out over the next five years, Sylling's fighter squadron, two more tof Phantom fighter-bombers and a fourth of forward air control aircraft will stay behind, prepared to keep America's promise to defend South Korea.

With 500 jet fighters - including 150 supersonic Mig-215 - the North Korean air force has a roughly two-to-one superiority in combat aircraft over the South Koreans.

From bases at Osan and Kunsan, respectively 25 and 120 miles south of Seoul, the U.S. fliers with roughly 100 planes keep the air-power balance. They have the capability of dropping nuclear weapons and could be dramatically supported and reinforced within hours by B-52s from Guam and fighter-bombers from the 7th Fleet.

Both sides train and wait and watch.

The North Koreans sometimes attempt to jam communications among U.S. planes and presumably follow American combat training flights by radar.

American intelligence officers monitor North Korean radio communications around the clock, study satellite photos, conduct electronic surveillance missions and use radar to analyze North Korean air-to-air tactics.

The overall evaluation, according to Air Force Lt. Gen. John J. Burns, is that "You're liable to have one hell of an air war here."

The North Korean pilots are rated as somewhat inflexible and over-dependent on vulnerable ground radar stations. Half their jet fighters are obsolete Mig-15s and Mig-17s of the same Korean War vintage as the F-86s still flying in the South Korean air force. Still, Burns says, the North Koren air force is large well-trained with combat experience in the Vietnam and Middle East wars on the side of North Vietnam and Egypt adn exhibits "a very aggressive nature in the air."

Burns, a stocky crew-cut veteran pilot decorated for combat missions in three wars - World War II, Korea and Vietnam - is now deputy commander of U.S. forces in Korea. He is confident. In the 1950-53 conflict, he says, the North Koreans used their small air force aggressively and were "decimated very quickly." The same tactics in a renewed Korean war would result in American air superiority in a week "or less," said Burns.

Scenarios written by U.S. Air Force planners for exercises usually end up with the North Koreans losing more than 50 per cent of their aircraft.

Sylling, married, 28, and a U.S. Air Force Academy graduate, is one of the pilots Burns expects to clear the skies.

In the restroom of the squadron's Osan offices, emergency flight procedures are tacked up over urinals and each toilet stall has a supply of air safety magazines. On the bulletin board there is a notice, "Dying for your country is a bunch of horse dung. Let the other bastard die for his country."

The message is clear, and Sylling, a flight leader and check pilot for the combat skills of other fliers, has a particular responsibility to minimize losses by accident or enemy action.

Of medium height with short, fair hair, Sylling has a steady gaze and a jaunty manner. He wears a black-and-white checkered scarf under the drab flight coveralls. He seems to fit his own description for the ideal fighter pilot - "aggressiveness tempered with judgment and ability."

His humor is nicely ironic. Designed in the mid-1950s, the Phantom is no longer new and it emits a conspicuous smoke trail - bad because the putative opposition, the Mig-21, is smokeless and hard to spot. "Our aircraft are painted like trees and they smoke like chimneys," he notes.

In a plane, Sylling is all business. The Phantom slipped the leash with an ear-splitting roar and leaped down the runway. The wingman was running just three feet away at 150 knots, and close enough to read the writing on the fuselage.

The ground haze and the water-logged landscape shrank away. In a block of space reserved for aerial wargames the two Phantoms took turns at running intercepts by ground control and onboard radar. Sylling's plane plunged through the air like a supercharged, supersonic roller-coaster, as he maneuvered for a radar lock-on and the chance to loose simulated air-to-air missiles or 'fire' a 6,000 round-per-minute 20-mm. gun.

The reporter flying in the weapons officer's seat behind Sylling swiftly succumbed to mal-de-mer as the world twirled and blurred. Weightless one second, pulling almost a thousand pounds in positive G-force the next, with the cockpit making no more sense to the inexperienced eye than the interior of a clothes tumble-dryer, Sylling was cucumber-cool.

In the staccato exchange of radio calls littered with numerals - altitude, distance, bearings, call signs - Sylling was terse as a short-order chef. In the exciting moments of the dog fight, his voice changed to a silky purr.

"Okay, I'm gonna' pull over here and take a heat shot at him."

There is a loud buzzing, and Sylling explains: "The missile 'looks' through the gunsight and when it sees an in-fra-red source, it growls. It's sitting out there on the wing saying 'Let me go, let me go!"

At 450 knots and 18,000 feet Sylling is playing the part of target.

"He's coming out of the sun, I suspect . . . There he is, back at seven o'clock, you got a smoke trail on the horizon about one fighter high . . . It's time to go up, make him overshoot."

Gravity comes on like electricity, and the pressure suit swells up to keep the blood out of the lower body and available to the brain.

"I got the burners kicking - there, can you fell them?" Under the after-burner thrust the Phantom surges forward like a lighted rocket. "I'm heading downhill . . . Mach 1.1 . . . supersonic . . . This is what we do every day - come out here and have at it"

Burns believes that air superiority is the first concern if war is resumed: We are going to have to win the air war wherever that takes us," he said. Under the strategy, that requires South Korean troops to stand their ground in prepared positions protecting the capital, Seoul, and its 1 million people, another high priority is close air support. The fighter-bombers squadrons practice attacking infantry [WORD ILLEGIBLE]artillery and tank targets in territory similar to the probable sites of any future battles.

Navigation beacons positioned along the Demilitarized Zone separating the two Koreas could guide U.S. bombers to targets as far as 200 miles into North Korea, day or night.

Within the limits of humanitarian concerns and political approval from Washington, Burns hopes that would happen: "If North Korea were to make the kind of mistake that would lead to hostilities . . . we ought to take out that big industrial base that she's been struggling so hard to build . . . If somebody wants to engage in war, they ought to pay for it."

The U.S. deputy commander and senior Air Force officer in Korea said it would be foolish to deny in advance the possible use of nuclear weapons, [WORD ILLEGIBLE] of power on the [WORD ILLEGIBLE] he said, "We don't [WORD ILLEGIBLE] [WORD ILLEGIBLE] says he doesn't want war, but [WORD ILLEGIBLE] he will carry out his mission with "vigor." He was born one year before the Korean War started, and doesn't want any nuclear holds barred if it resumes.

Sipping a drink in the officers' club at the end of a typical 12-hour workday, Sylling explained: "When those things are around, you find out how determined people really are."