After several days of rainfall, Thursday dawned clear and bright, ideal weather for the iron workers who are constructing a huge cylindrical cooling tower at the Pleasants Power Station here.

Fifty-one men were clambering over scaffolds up to 170 feet in the air, as concrete was poured for a new level on the half-constructed tower.

Shortly after 10 a.m. witnesses heard a rumble, a sound described by one as that of "rolling thunder," punctuated by screams. The scaffolds had collapsed, and all the men on them were killed, their bodies lying in a twisted mass of metal and wood stacked six to 10 feet high.

West Virginia Gov. John D. Rockefeller's office called it the worst non-coal-mine construction accident in the history of the state and possibly the United States.

A rescue worker from nearby Newport, Ohio, was one of the first on the scene and said he found bodies scattered all along the inner perimeter of the tower.

"It was a lot of blood, guts and gore," said another rescue worker.

Witnesses said the scaffolding, which hung on the top of both the inside and the outside of the tower and which encircled it, peeled off "like a bunch of dominoes falling."

"It went like a chain reaction" said one nearby resident.

The Associated Press reported that Lyle Corder, a spokesman for Monongahela Power Co., which operates the power plant, said the men had poured the 28th layer of concrete Wednesday and were working on the 29th layer yesterday morning.

"As the 29th was being poured today, the 28th disintegrated and the bolts that were holding the scaffolding pulled loose away from it," Corder said. A Monongahela Power spokesman said the diameter at the base was 360 feet and the tower was to be 430 feet tall when finished.

In Washington, D.C., a spokeman for the Occupational Safety and Health Administration said 13 inspections of the Pleasants Power Station site since 1973 had revealed "numerous violations, both serious and non-serious," but he said he did not know what they were.

Spokesman James Foster said the most recent inspection was a year ago and that the operations of Research Cottrell Inc., the subcontractor building the tower, had never been inspected.

In Bound Brook, N.J., Thomas Buentune, director of corporate communications for Research Cottrell, said the company inspected the scaffold daily. He said it was "a complete mystery how this can happen . . . it's impossible."

In Belmont, W. Va., about four miles north of the accident site along the Ohio River north of Parkersburg, word of the tragedy spread quickly. Many local families had more than one relative among the 1,000 men employed at the construction site, and members gathered at the volunteer fire department building which had been made into a makeshift morgue.

Maxine Johnson of Belmont lost a brother, four nephews, and four other relatives in the collapse. Her nephew Bob Steele, said, "I had four brothers and now I'm the only one left."

Many of the dead workers were from Belmont, a town of about 1,000. The Rev. Ernest Hammock, pastor of a Baptist church in the community, knew some of them.

"They were just decent, hard-working people," he said. "A lot of them just went wherever they could to get a job."

The tower is to be part of the coal-fired power plant complex that draws in river water to make steam. When completed, the tower will be used to cool the water before it is returned to the river.