The opening battle in what could become a new series of labor wars in the steel industry is being fought on the banks of the muddy Ohio River, where Ray Fisher and his father and grandfather before him have poured molten steel for Wheeling-Pittsburgh Steel Corp.

"I have watched five men die with my own eyes inside that steel mill," said Fisher, 51, a 27-year veteran, "I have seen dozens of men get burned bad. It's rough in there . . . . And now they want to cut our pay, and pay the people who bag groceries as much as we make. No way."

The first major steel strike in 26 years began Sunday after the bankrupt Wheeling-Pittsburgh, the nation's seventh-largest steelmaker, canceled its union contract and imposed an 18 percent reduction in wages and benefits on 8,200 workers at nine mills in Ohio, Pennsylvania and West Virginia. Average base wages were cut from more than $11 an hour to $8.10 -- or more than $125 a week -- and vacations, holidays and medical insurance coverage were substantially reduced.

The dispute here has the dimensions of a death struggle, according to both sides.

Wheeling-Pittsburgh, the largest steel firm to declare bankruptcy, says that if the strike persists, it will be forced to cease operations, liquidate its assets and terminate pension plans. The company canceled medical insurance for strikers Tuesday.

Steelworkers generally dismiss company statements as scare tactics but say that they would risk their jobs anyway because the cuts are too severe to tolerate for union members who have given up wages and benefits totaling more than $15,000 per worker in the past five years.

The stakes are particularly high for the United Steelworkers of America because the nation's Big Five steel makers, which employ most of the remaining 200,000 unionized steelworkers, have served notice that they will break a 30-year pattern of "coordinated" bargaining and individually seek substantial new concessions as contracts expire in 1986.

"Every other company is getting in line behind Wheeling-Pitt and is ready to say 'Me too' on seeking givebacks . . . . It is going to get rough," said a steelworkers union spokesman.

"We are ready for this war . . . . I look for a long work-stoppage," Paul M. Rusen, the union's chief negotiator, told a cheering crowd of 3,000 union family members who packed a sports arena here Monday.

The Wheeling-Pittsburgh case also is being closely watched by labor and management for another reason. It is the first major cancellation of a union contract since federal bankruptcy laws were tightened last year to place a higher burden of proof on companies to show that scrapping contracts is necessary for survival.

Bankruptcy Judge Warren W. Bentz in Erie, Pa., in a July 17 ruling that is being appealed by the union, said revocation of the union contract was justified as part of a company plan to pay off more than $500 million in overdue debts.

Much of that debt was incurred in the past few years in a massive modernization program that the company said would restore profitability.

Hot and dangerous work and a once-strong union helped make Ray Fisher's father and grandfather the high-paid envy of other workers from the 1940s through most of the 1970s. But recessions, cheaper foreign steel and union concessions worth $3 billion in the 1980s have locked the current generation of steelworkers into a cycle of downward mobility.

"We were accustomed to a pretty lucrative life style in Steel Valley. The average guy makes $24,000 to $26,000 . . . . And we are not going to set labor back 30 years by working for slave wages" of less than $20,000, said Charles Stock, 33, a blast furnace operator and local union official.

The union calculates that after-tax wages under the company plan would be about $6 hourly. "And I can't raise three kids on that," Stock said. He said he expects to lose his mobile home and two cars if the strike lasts, but he added that he would also lose them if it ends with concessions.

Company spokesman Ken Maxcy, a 32-year employe, said Wheeling-Pittsburgh enjoyed good labor relations until the specter of bankruptcy emerged last year. "We tried to bargain these concessions, but we got nowhere," he said. The union forced the bankruptcy in April, he said, by refusing concessions unless the company received similar concessions from its creditors, primarily banks and insurance companies.

"The question, to us, was whether the banks are going to get well at the expense of the workers," said union spokesman Richard Fontana. "The creditors will be the first ones who get paid off, and simultaneously the workers lose."

Under the court-approved plan, combined wages and benefits were cut from $21.40 an hour to $17.50. Maxcy said the ruling could have allowed the company to cut to $15.20, but it chose not to. "We are not attempting to break the union, we are only making whatever changes are necessary to emerge from bankruptcy" and save the company and its jobs, he said.

But to many steelworkers, the concessions would be tantamount to busting the union. "My dad fought for this union, and my granddad died just as the union was getting strong . . . . Now we're losing it," Fisher said.

The 190-page union contract, which governed Wheeling's work force for more than 40 years, was to be replaced by a nine-page company wage-benefit plan.

"We fought hard for what's in that contract. You bought your new cars and your homes, and you planned your life based around those contracts" every three years, said Ted Van Horne, a white-haired veteran, whose eyes filled with tears as he described 34 years at Wheeling-Pittsburgh.

"Steelworkers have been the greatest industrial union. This is the beginning of trying to break the Steelworkers," Van Horne said. "If they can break us here, they break us anywhere."