Michael Andretti took advantage of his father's continued hard luck to win the Marlboro 500 yesterday at Michigan International Speedway in Brooklyn, Mich., the fastest 500-mile race in Indy-car history.

The younger Andretti inherited the lead when Mario Andretti, the 1984 winner here, fell out of the race with an engine failure after building a two-lap lead over his son just past the halfway point of the 250-lap event.

Michael, 24, easily held off Indianapolis 500 winner Al Unser and Bobby Rahal over the last 94 laps to gain his second victory of the season, the fifth of his blossoming Indy-car career and his first triumph over 500 miles.

Andretti averaged 171.490 mph in a race slowed by only two caution periods. That was faster than the 170.722 run by Rahal in winning the 1986 Indy 500, the previous fastest Indy-car race.

Andretti crossed the finish line 9.11 seconds ahead of Unser, who edged Rahal for second place. Danny Sullivan was fourth . . .

A showdown between Grand National stock car stars Bill Elliott and Bobby Allison was washed out in Nelles Corner, Ontario, when rain forced organizers of the Molson Export 300 event to reschedule their program for today. Allison will be on hand for the race, but Elliott had to pass because of prior commitments.

his right arm.