ROMULUS, Mich. (AP) _ A jetliner clipped another while preparing to take off from the Detroit airport in heavy fog Monday, igniting a fire that left one plane in smoking ruins. Eight people were killed and at least 21 injured, officials said.

It was not immediately clear what caused the collision between a DC-9 and a Boeing 727-200, both operated by Northwest Airlines. A spokesman for air traffic controllers said the DC-9 appeared to have become lost on a slick, foggy taxiway and strayed into the 727's path.

For nearly an hour after the accident, smoke billowed out of the fuselage of the DC-9, where passengers apparently became trapped by the fast-moving fire. By the time the fire was extinguished, much of the plane's roof was open to the overcast sky.

Officials had initially said that 19 people were killed, but Northwest officials and Wayne County Executive Edward McNamara later said that was wrong.

McNamara said the medical examiner had ''swept through the wreckage twice'' and found eight bodies.

Northwest spokesman Doug Miller said the airline had checked passenger lists and accounted for everyone except eight people, who were presumed to be the victims. He said 21 people remained in hospitals Monday evening.

The DC-9, Flight 1482 to Pittsburgh, was carrying 39 passengers and four crewmembers, according to the airline. The 727, Flight 299 to Memphis, was carrying 146 passengers.

Both flights had originated in Detroit, said Patrick McCann, a Northwest spokesman at its headquarters in Eagan, Minn.

''Apparently the right wing of the 727 hit the aft section, the engine, of the DC9, taking the engine off,'' said Alan Muncaster, another Northwest spokesman. ''That resulted in the fire. That, at this point, is all we know.''

At the time of the crash, visibility was poor and the ground was wet from a morning snow and sleet storm that delayed flights at Detroit Metropolitan Airport. Muncaster said the airport had been closed to inbound traffic but that planes were being allowed to take off.

Tony Dresden, a spokesman for the National Air Traffic Controllers Association, a union representing air traffic controllers, said there was about a quarter-mile visibility in the air, but only about 800 feet on the ground.

''We've had some discussions with our people out there,'' Dresden said. ''The DC-9 pilot became lost on the runways. The pilot gave the ground controller erroneous information about his position and turned right onto the runway where the 727 was taxiing.

''The DC-9 pilot discovered at the very last moment where he was, and so the ground controller told him to immediately get off that runway, but it was too late.''

He stressed that his information was preliminary. The Federal Aviation Administration, which supervises air traffic controllers, did not immediately comment about Dresden's statement.

Investigators from the National Transportation Safety Board were being dispatched to begin a probe aimed at determining the cause of the accident, a safety board spokesman said.

One survivor from the DC-9, 41-year-old John Izzo, said he was dozing when he ''heard a bang, felt a thud and then all of a sudden, there was a blast.''

''I saw the fire to the right rear. The whole top burned away, but something was definitely blown away because something flew over my head,'' said Izzo, a Westinghouse nuclear engineer who was returning to Pittsburgh from a business trip.

Izzo said he escaped by jumping from a wing to the ground. He was not hurt.

''The people that made it down and out were crawling through the slush into the middle of the field,'' he said. ''I just watched the fire spread across the plane and engulf the entire fuselage.''

Izzo said he was seated in Row 10 and believes people in the rows behind him could not get out.

''The only thing going through my mind was 'I'm going to die in this damn plane and I'm only 26 years old,''' said another passenger, medical student Mike Marrone of Saddle River, N.J.

''I wanted to get out of there and I think a lot of other people did too. I didn't see too many acts of heroism,'' Marrone said.

The body of the 727 did not appear to have been seriously damaged in the collision. One passenger, 60-year-old Robert Karp of Jackson, Miss., said passengers from the 727 walked off the plane and down the stairs.

''It sounded to me like it was a loud thump,'' said Karp, a professor at Jackson State University.

''I thought the tire had blown out. The front end of the plane had begun to lift off. I don't think the back wheels were off the ground yet. As soon as I heard the thump we came to an abrupt stop. I remember looking at the other plane and seeing smoke rolling out.''

Three men who earlier had identified themselves as pilots were sitting across the aisle from him. One of them said, ''Oh, my God, our entire wing is gone,'' according to Karp.

McNamara said the only injuries on the Boeing were those that occurred during the plane's evacuation.

Muncaster said the DC-9's pilot and co-pilot were injured, but the pilots of both aircraft were able to provide statements for authorities. Northwest did not reveal what the pilots said.

The 727 ''wasn't airborne'' but was ''on a takeoff roll,'' Muncaster said, but could not estimate how fast it was traveling. Its passengers evacuated through the rear of the plane, whose right wing was sheared off, he said.

Linda Kalinsky of the Taylor Ambulance Co. said there were 50 or 60 injuries altogether, including some burn victims.

Twenty-one injured were taken to four hospitals in the area, including two who were taken to the University of Michigan Medical Center Burn Center at Ann Arbor.

Muncaster said surviving passengers were taken to the airport Marriot hotel, where a family center was set up.

As dusk settled in around 4 p.m., a stand of huge lights were wheeled into place near the cockpit of the DC-9 on Runway 3C to allow firefighters and investigators to see.

At about 5 p.m., rescue workers hoisted body bags from the DC-9 and handed them to others on a wing.

In Northwest's offices at Greater Pittsburgh International Airport, 12 to 15 people waited for information on family members and friends, said Bruce Nelson, director of sales and marketing for the airline's Pittsburgh office.

''They are very quiet,'' Nelson said at a news conference. ''They've just been told that we're trying to get a passenger list and get things in order.''

Romulus, about 10 miles west of Detroit, was the site of the second worst air crash in U.S. history, the Aug. 16, 1987, crash of a Northwest MD-80, on takeoff in which 156 people were killed.