Alain Prost, the leader in the Formula 1 point standings, won the pole position yesterday for today's inaugural Grand Prix of Detroit.

The Frenchman drove his yellow, black and white turbocharged Renault to a lap of 82.700 miles per hour in the first of two 60-minute qualifying sessions, then saw his position at the front of the 26-car field solidified by a persistent afternoon rain.

The cool, wet weather, which held down the crowd at the downtown race course to about 15,000, also left intact all the morning qualifying times on the 2.5-mile, 20-turn track. The race will run 175 miles or two hours, whichever comes first.

Missing from the field will be defending world champion Nelson Piquet of Brazil, whose BMW-powered Brabham blew an engine early in the morning session . . .

Terry Labonte gained the pole position for today's $250,000 Van Scoy 500-mile stock car race at Pocono (Pa.) Raceway without putting a foot on the throttle.

Rain and fog prevented NASCAR from holding a Grand National qualifying session for the first time since the Atlanta time trials were washed out in 1973. Labonte, in a Chevy, gained the pole by virtue of his lead in the car-owner point standings.