A pit fire spoiled a strong showing by Al Unser Jr. yesterday and allowed Danny Sullivan to gain to his first victory of the season and third of his career in the Cleveland Grand Prix.

Unser led all but six of the first 62 laps at Burke Lakefront Airport and appeared on his way to victory before he made what was supposed to be a routine stop.

As his crew serviced the Chevrolet-powered Lola, it appeared the nozzle on the fuel hose missed its receptacle on the side of the car. Methanol from the hose splashed onto the car and burst into flame. Unser, who had his helmet visor up as he took a drink, was sprayed with fuel, irritating his eyes. Four crewmen were burned before they could be splashed down with water.

Unser had only singed eyebrows. He was flown by helicopter to University Hospital for a chest X-ray and observation, but was expected to be released.

Paul "Ziggy" Harcus of New Zealand and Mike Arnold of Albuquerque were flown to Cleveland Metro General Hospital. Officials said both had first- and third-degree burns. They too were expected to be released. Gary Armentrout of Fresno, Calif., and Brian Barnhart of Indianapolis were treated at the track's medical facility and released.

Sullivan, who had been running just over one second behind Unser, inherited the lead. "It would have been a tough battle," he said. "I don't know if I could have gotten Little Al."

Sullivan led the rest of the 85-lap, 201.4-mile race in his Penske 90 Chevrolet. Bobby Rahal was runner-up, 5.02 seconds back.

Defending champion Emerson Fittipaldi was third, followed by Mario Andretti and his nephew, John Andretti. . . .

Darrell Waltrip remained in serious but stable condition in a Daytona Beach, Fla., hospital, where he has been since suffering a broken left leg and left elbow Friday in practice for the Pepsi 400. . . .

Alain Prost burst past Ivan Capelli with two laps left in Le Castellet, France, for his third straight French Grand Prix victory. The Frenchman gave Ferrari its 100th victory in Formula One racing, and it was Prost's second straight, giving him 42 for his career.

Prost trailed Capelli for 77 of the 80 laps on the 2.37-mile circuit in a forest near Marseille. On Lap 78, Prost cut inside of Capelli just before a double right-hand curve, hit the accelerator and shot into the lead, winning by 8.8 seconds.

"It was the only place possible I could do it without risking second," Prost said.

Ayrton Senna of Brazil was third in a McLaren-Honda, keeping the lead in the seasonal standings with 35 points.