Given the number of Porsches entered, their history of superiority in endurance racing and performance in qualifying here, the main question when the 24 Hours of Daytona began yesterday appeared to be not which car would win, but whose.

Turbocharged Porsches dominated trials and practice sessions last week, and occupied 11 of the first 12 positions on the grid for yesterday's rolling, paced start. The green flag, signaling the start of the longest endurance test in American racing, came down at 4:33 p.m.

There were a dozen Turbo Porsches in the starting field of 67 cars. The odds on one of them winning the $17,500 first prize seemed prohibitive - even though two encountered severe turbocharger problems within the first 45 minutes.

The Porsche 935 that Danny Ongais drove to the pole position in rain-slowed qualifying on Thursday led through a speedy first 14 laps, then crawled into the pits in a melancholy swirl of smoke.

The jet-black, red-striped Interscope Racing entry, which Ongais was driving with owner Ted Field and journey-man Milt Minter, promptly lived up to its history of speed but unrelability.

After a near-record time on the 14th lap, it blew a turbocharger, and gave up seven laps as the crew worked furiously to change it. Returning to the course, the car continued to limp and smoke, and was brought back into the pit for an engine change, at a cost of $35,000.

The first casualty had been the Porsche 935 driven by Italian Carlo Facetti. It burst into flames during the sixth lap and came to rest midway down the front straightway.

Since repairs on the course can only be done by the driver, the Facetti-Martino Finotto entry of Italy's Jolly Club appeared finished early.

With Ongais frustrated in the garage area, the turbo Porsche driven by Rolf Stommelen of West Germany took the lead. He held it through the first 50 laps.

This 935, codriven by Antoine Hezemans of The Netherlands, was the second entry of the JMS Brumos Prosche team headed by the three-time champion Peter Gregg. The 37-year-old Harvardian owns a Porsche dealership in Jacksonville.

Stommelen, 35, one of the world's leading distance racers, set a lap record on the sixth trip around the 3.84-mile course. The Daytona International Speedway combines a long stretch of the steeply banked trioval used for the Daytona 500 with a flat, twisting road portion that requires 17 gear shifts.

Stommelen sped around it in 1:51.546 minutes, averaging 123.931 miles per hour. The old record was 1:52 flat, an average of 123.42 mph, set last year by Belgian Jacky Ickx, who also drove a Porsche 935.

Ickx was supposed to drive here this year, sharing the wheel of another turbo Porsche with owner Dick Barbour and two-time Indianapolis 500 winner Johnny Rutherford. But he hurt an arm in a skiing accident last week.

Ickx was replaced by Manfred Schurti of Liechenstein, who was expected to keep the team competitive. He was at the whel when a tire exploded on the 36th lap, spewing fragments of fiberglass, rubber and other debris at the entrance of pit row.

This mishap, which occurred in waning daylight, seemed to shelve the Barbour entry even before Rutherford had a turn at the wheel. Rutherford earlier said he plans more road racing this year. His impressive career has been devoted mostly to oval tracks.

The debris on the course prompted several complaints as darkness enveloped the speedway.

The Stommelen lap record did not last long. Defending champion Hurley Haywood, who won in 1973-75 with Gregg and last year became the first man to win the 24 Hours here and at Le Mans, France, surpassed it on the seventh lap. His time was 1:51.151, an average of 124.371 mph.

Haywood, who helped drive a Porsche Carrera to victory with John Graves and Dave Helmick last year, is sharing the controls of a turbo 935 with Bob Hagestad this year. He started at the back of the pack but climbed to second place within an hour before losing four laps to a pit stop.

The Haywood car never made the qualifying because of persistent electrical problems. These were eventually traced to a faulty $1.25 coil resistor. Chief Steward Charlie Rainville permitted Haywood to start, however, and he challenged for the lead before encountering more of the problems that had made the last week so discouraging.

The yellow caution flag came out after the Nova driven by Tim Chitwood crashed into the wall at the east end of the speedway at 6:30 p.m. Chitwood was injured, but his demolished car was too close to the racing surface.

The safety car was employed to slow the field, a first for 24-hour racing. This left the cars lined up nose-to-tail when the race was resumed 10 minutes later.

After 60 laps, the average speed was 116:187 mps. The Gregg entries were running 1-2 Hezemans had taken over from Stommelen. He was leading his stablemate - driven by Gregg, to be spelled by Claude Ballot-Lena of France and Brad Friselle - by less than one lap.

The turbo BMW 3201 codriven by David Hobbs of Britain and Ronnie Peterson of Sweden had a short day.

Hobbs started from the third position on the grid and quickly moved into second place, then fell behind with engine problems. Shortly after Peterson took over, less than two hours into the race, while smoke billowed from the right side of the car Peterson retired with the car's third blown engine of the week.

The factory-backed team, still bewildered as to what was going wrong, had no engines left.

A Porsche victory seemed more certain than ever