The first 900 of 5,000 Youngstown steel workers to be put out of work filed slowly out of the factory gates in the dark today, a steady stream of silent men carrying lunch pails.

By morning light, the smoke had ceased pouring from the slender smokestacks, and the open hearth furnaces which had blazed for 77 years, keeping this Mahoning River Valley community alive, were empty an cold. Only the slag heaps retained a glow.

The layoffs were announced Monday by Youngstown Sheet and Tube Co., which said it will furlough 5,000 of its 8,400 men. The announcement sent tremors through this steel-dependent valley.

About 900 employees lost their jobs between Friday and Saturday, 400 of them in the shutdown of the open hearth furnaces, where the iron ore was mixed with alloys and scrap metal and turned into steel ingots. Of the 12 open hearth furnaces in the plant, only four had been operational in recent months.

The existing stock of steel is sufficient to fill existing orders, but new orders will be filled from the Brier Hill plant seven miles away.

Hardest hit is Struthers, a Youngstown suburb which sits grimly across from the plant, a community already riddled with vacant storefronts. Bankers there were receiving calls to cancel car and home loan applications. Foot traffic in the downtown shopping area was slashed in half after the announcement, merchants said.

"It's a ghost town. It doesn't take much more to see the tumbleweeds rolling down the street," said furniture salesman Howard Maurice.

Some steelworkers blame the job loss on the company's parent corporation, Lykes Corp., claiming it failed to make capital improvements at the plant and bled the resulting antiquated operation of its assets. "They took all the money out and ran away and left us hungry," said steelworker Anthony Frattaroli in a heavy Italian accent.

Other say environmentalists exacted too high a price for compliance with air and water standards. "I blame Nader too for opening his yap every time," said one man who lost his job yesterday morning.

The impact of the shutdowns on Youngstown's economy was clear. Youngstown's daily newspaper, the Youngstown Vindicator, carried six stories about layoffs in the steel industry on its front page yesterday.

Nearly all said they felt the government had betrayed them in allowing cheaper steel to be imported from abroad at the expense of American jobs. "I was a Democrat. Nixon was bad but at least I worked good under him," said a steelworker.

Most of the 8,400 plant workers still do not know who will be among the 5,000 to lose their jobs.

"There's is a lot of anxiety as to who's getting it and when. We just got to wait and see. What comes will come," a gravel-voiced steelworker said.

Even employees with 30 years in the plant will first learn of their unemployment from the weekly shift listings posted on a bulletin board. If a man's name is not on next week's roster, he is without a job. No letter from the company, no advance notice.

"That's just the way they do it in the steel business. It's always been that way," said a company spokesman.