Five workmen were killed and 15 were injured today when the roof of an $8 million stadium under construction near O'Hare International Airport suddenly collapsed "like a whole lumberyard falling down" moments after a jetliner reportedly roared overhead.

The wooden roof of the rectangular, four-story stadium, which was designed to seat 19,400 people, came crashing down about 8:30 a.m. while 26 men were at work, police said.

"It was just like a war...everything was coming down around us," said electrical contractor Victor Molinilli, 38, of Mount Prospect.

Molinilli, who was among the injured, said he was working in a trench under the grandstand area. He said there was no warning the roof was about to come down.

The cause of the cave-in, which witnesses said came moments after a jet flew over, is under investigation.

Spokesmen for the architect and the Federal Aviation Administration said it was too early to speculate on whether the plane had anything to do with the collapse. An FAA official, however, said he was certain a large jet would have been landing at O'Hare at the time of the accident.

Mayor Donald E. Stephens said he talked with some construction people and that he believed there was nothing to indicate the plane caused the collapse.

The stadium collapse was the second in the United States in less than three months.

The roof of the 17,000-seat Kemper Arena in Kansas City, Mo., caved in June 4 during a severe thunderstorm. Buffeting winds, metal fatigue in two key steel bolts and a flawed design were cited in the collapse of that arena, site of the 1976 Republican National Convention. Neither the Kemper's design, nor its architect, is the same as the Rosemont stadium's.

In January 1978, the snow-laden roof of a sports coliseum in Hartford gave way just hours after 5,000 spectators went home from a basketball game.

The stadiums were empty and there were no injuries in those two incidents.

The Rosemont stadium, which had been scheduled to open in late December, was designed for sporting events, circuses and business meetings.

Joseph Peterson, spokesman for the Rosemont Police Department, said five men were confirmed dead. All were taken to a temporary morgue across the street from the stadium.

The dead men, all carpenters, were identified as Arturo Reyes, 30, of Chicago; John Geib, 30, of Franklin Park; Martin Wilkensen, 36, of Elk Grove Village; Chester M. Phillips, of Des Plaines; and Douglas E. Wilson Jr., 25, of Chicago.

Peterson said many of the workers were trapped in the wreckage but were later freed.

One witness, Paul Prorok, said the collapse "sounded like a whole lumberyard falling down."

Prorok, employed by a nearby firm, said he had been watching carpenters covering laminated wood beams with plywood when the roof gave way. The stadium's roof was supported by laminated wood beams set into concrete pillars.

"There were about 18 men working on the roof when a plane came over," said James Pinkston, 43, a concrete worker. "Suddenly, everything began to vibrate. You could hear the roof cracking and then it started falling in."

A spokesman for the FAA, Neal Callahan, said planes were flying "just a couple hundred feet" over the site this morning.

Rescue crews from Chicago and seven suburban communities were sent to the stadium, northwest of Chicago near the giant airport.

Fred Schroeder, an architect with the firm of Anthony R. Rossi, which designed the stadium, said it was "very wild and very premature" to speculate on whether the plane could have triggered the collapse of the roof.

Callahan said he had never heard of airplane turbulence causing any destruction on the ground although "large jets do give off mini-tornadoes, as we call them."

He said the stadium is 65 feet high but that the original plans had called for a taller structure. He said building representatives met with FAA officials in 1973 about the planned size and location of the building.

Chris Sharpels, a service station attendant who was working about 150 yards from the stadium, said, "The roof came down in a terrible crash. I heard this terrible roar like a crash, and the ground shook for a little while. When I turned to look at it, the roof was gone and people were running around everywhere."

Dave Beatty, who was sitting in the Sheraton-O'Hare Motor Inn about 200 yards from the stadium, said, "One minute I was looking out the window, I turned away and I looked back and it looked as if someone dropped a huge weight into the center of the building." CAPTION: Picture 1, Firemen carry injured worker from rubble of stadium at Rosemont, Ill. AP; Picture 2, Rescue teams wait as crane lifts pieces of roof of killing five workmen; Picture 3, a construction worker stadium that collapsed yesterday at Rosemont, Ill., weeps beside the body of a friend. AP