WITH U.S. FORCES, SAUDI ARABIA, FEB. 4 -- A quartet of sleek F-16A fighter-bombers was on its way today to drop loads of cluster bombs on Iraqi military targets. But first, the U.S. warplanes nosed in for an aerial "pit stop."

The jets streaked out of the sky at 21,000 feet above a swath of empty desert near the Iraqi border. Slowing on approach, they glided effortlessly into place at 400 miles an hour behind the lumbering KC-135 airborne gas station.

One of the four peeled gently away from his squadron and slid toward the fuel-delivery boom dangling from the flying tanker's tail assembly. Carefully trimming speed and attitude, the pilot held his fighter steady while Airman 1st Class Clayton Izumi, lying prone in his niche at the tip of the KC-135's tail, maneuvered controls that directed the boom nozzle into a refueling hole behind the F-16's cockpit canopy.

With the nozzle locked into place, pumps aboard the tanker pushed 615 gallons of jet fuel into the F-16, culminating another in the endless series of aerial refueling ballets that have made the Persian Gulf conflict a war like no other wars.

Routine aerial refueling on an unprecedented scale has helped U.S. and allied air forces mount more than 44,000 sorties in the 19 days since their massive bombing campaign began against targets in Iraq and occupied Kuwait. That has meant about one sortie -- one mission by one plane -- per minute, at least half of them combat flights.

The air commander for Operation Desert Storm, Air Force Lt. Gen. Charles A. Horner, said that coordinating the multiple refuelings necessary for such a high rate of sorties has been his biggest steady headache since the war began.

"Getting enough fuel up to get them to the target and back" has been difficult, he said in an interview, because of the heavy payloads of bombs and missiles carried by U.S. and allied warplanes and the relatively short range of most modern fighter-bombers being used in the war.

Taking off from bases in Saudi Arabia or carriers in the gulf area, aircraft have been refueling once on the way to their targets, then a second time on the way back, to give them longer time over enemy territory. Directed by AWACS airborne radar stations, they have been able to rendezvous with fuel tankers at predetermined points just off the battlefield.

The F-16s that nosed in for fuel today were heavily laden with cluster bombs. Two canisters were racked under each wing, ready to spew their dozens of deadly bomblets on Iraqi troop concentrations in Kuwait or supply convoys trying to run the gantlet with food and munitions from Iraq.

The bombing campaign, which began with an onslaught against military command and control centers deep in Iraq, has shifted emphasis in the last 10 days to destruction of supplies in and near Kuwait and disruption of well-trained Iraqi Republican Guard units stationed in southern Iraq near the border with Kuwait.

Marine Maj. Gen. Robert B. Johnston, the Central Command's chief of staff, said that 250 of the 2,700 sorties flown in the last 24 hours were directed against Republican Guard emplacements. These included 26 separate waves of fighters, such as the F-16s, and six waves of high-altitude B-52 bombers.

The relentless bombing has been described as the best hope for dislocating and demoralizing the Republican Guards and cutting them off from command centers in central Iraq and, in the other direction, from the Popular Army conscripts manning trenches and minefields just inside Kuwait.

At best, senior U.S. officers have said, the effort could so traumatize Iraqi troops and damage their equipment as to force surrender. Or if they hold firm, the officers added, the bombing will have weakened Iraqi defenders enough to hold down U.S. and allied casualties in any ground assault on Kuwait.

Cluster bombs, which break up into many smaller bombs able to devastate an entire area, have been a key weapon in this effort. Stubby green pods with a visible seam down the middle, they hung beneath the F-16 wings at an angle, leaning away from AIM-9 Sidewinder air-to-air missiles that tipped the ends of both wings.

Pilots in the cockpits below -- Darth Vader figures behind flight helmets, tinted visors and oxygen tubes -- offered terse waves as they read "full" on their fuel gauges and banked away to begin their bombing runs. The three groups of four planes that pulled close to refuel were from a New York State National Guard unit. Some sported "The Boys from Syracuse" painted on their tails.

Izumi, a 22-year-old from Radcliff, Ky., said the need for radio silence often prevents him from communicating with the pilots. Instead, they read his signals from lights on the KC-135. At times, however, chatter has sprung up before and after the bombing raids. "If they're going out, when I talk to them, they're very serious and kind of quiet," he said. "On the way back, I guess the stress is over, and they're joking and laughing."

Although U.S. military censorship rules bar reporting the number of refueling flights today in the gulf war theater, Izumi's tanker unit alone has flown more than 1,000 sorties to fill up more than 4,000 warplanes since the conflict began.

The tanker wing commander, Col. David E. Cormack, 46, of Abilene, Kan., said the pace has strained his pilots and the maintenance schedule for his aircraft but that none has gone down. A 125-hour per month limit for pilots' flying time has been waived, he added. "We've done more flying since the war began than a tanker crew would do in nine months back in the United States," he estimated.