THOUSANDS OF avid football fans will cross picket lines today and tomorrow in 14 major league cities to watch teams of strikebreakers compete in an event that sends a chilling message to the American worker: You are all replaceable. No matter who you are, or what you do, or how skilled or highly paid -- you can be replaced.

It is too soon to tell whether the National Football League owners will succeed in their risky gamble of fielding strike-replacement teams -- whether they can lure fans to clearly inferior games, keep the support of the TV networks and big-ticket advertisers, and, most importantly, eventually induce enough big-name players to cross their union's picket line and break the strike.

Regardless of the outcome, the NFL owners' attempt is a fitting finale for the 1980s, a decade in which the American worker, especially the union worker, has taken a bashing -- thanks in large part to the antiunion tone set by the Reagan administration and by militant corporate management which has declared that the American worker, skilled and unskilled, is expendable.

The replacement of some of the nation's most gifted and highly paid athletes -- average salary $230,000 -- may elicit little sympathy from the average worker. But many workers have learned from hard experience that the NFL strike is only the latest in a steady progression of events that have made this the decade of the marginal employe.

Labor has always been considered replaceable by those with capital. In the decades of labor strife since the 1920s, however, it was usually only the less-skilled who could be easily replaced: The old steel mill and coal mine owners would import Italians, Irish, Chinese, as well as black Americans as strikebreakers. Higher-skilled workers were usually considered too valuable and difficult to replace -- especially in an era when many Americans honored picket lines and would not risk being labeled a "scab" who takes away a striker's job.

But that was yesteryear. In a succession of blows to organized labor in the 1980s, highly skilled machinists, experienced meatcutters, copper miners, bus drivers, airline pilots, telecommunications technicians -- and, of course, the entire network of 11,000 federal air traffic controllers -- have been replaced by strikebreakers in case after case.

Even stardom is no deterrent to being replaced by cost-conscious management. Consider the recent case of popular television actress Valerie Harper, who starred in her own show "Valerie," until she had a contract dispute with NBC. NBC is owned by General Electric, which in past decades maintained a notoriously antiunion philosophy, and which currently is breaking a strike by more than 2,000 union technicians at NBC.

When Valerie Harper held out for more money, NBC killed her: The Valerie character dies and is replaced by actress Sandy Duncan, who plays her sister. The show has been renamed "Valerie's Family" with the expectation that the public will buy a lesser product.

And so it is with the football owners, who operate a monopoly with guaranteed multimillion-dollar revenues, and are asking the public to accept a clearly inferior product in the interest of the NFL's conquering its uppity union once and for all.

The unique thing in this case is the highly publicized nature of the strike, according to Thomas Kochan, professor of industrial relations at Massachusetts Institute of Technology and a leading authority on American management. "It is one thing to replace people in a paper mill or an oil refinery, where maybe you can't tell one set of products from another. But we certainly can tell an all-pro quarterback from some guy who got cut two years ago," said Kochan.

"That owners are willing to engage in this kind of risky strategy says something about where they think the public has moved, that the public would accept this kind of tactic," Kochan said. "It's another sign of the erosion of the strike, and the sanctity of the picket line in the eyes of the public," since many people are apparently willing to cross the line.

But it should come as no surprise that Pro Football Incorporated has come around to a strategy that the rest of the corporate world has been employing with increasing frequency since 1981. That was when President Reagan employed strikebreaking as a national strategy in firing and replacing the air controllers, who had violated the law by striking.

"When the president of the United States did what he did on Aug. 5, 1981, that's when the tide turned," said AFL-CIO spokesman Rex Hardesty, "Once the message was assed by the president that strikebreaking was the way you handle unions, that became a more widespread attitude."

Replacement of strikers has become commonplace, practiced by companies such as Continental Airlines, TWA, Greyhound, Iowa Beef Processors, AT&T, the Chicago Tribune and The Washington Post, to name just a few.

Corporations -- driven by intense foreign competition, by the economic turbulence evident in the Wall Street takeover frenzy, and by the constant quest for higher profit -- have employed other, newer varieties of cost-cutting strategies when it believes that the price of labor is too high.

Companies have replaced tens of thousands of union auto workers by "outsourcing." Most of your Ford or Chrysler is no longer made by a UAW worker, but more likely by a foreign worker. Companies have also "contracted out" every conceivable variety of job -- from a steelworker to a county prison guard, cheaper employes can be found by hiring outside companies to replace higher-paid steady workers. And part-time and temporary employes -- who often receive no health benefits -- have been used with increasing frequency to replace that old, more costly commodity, the fulltime worker with benefits.

In the football movie "North Dallas Forty," an aging football player played by Nick Nolte is stung by the abusive way he is treated by management. In frustration, he tells a teammate: "You know, we're just the equipment."

If that kind of attitude becomes widespread, then U.S. companies could have big trouble with an unhappy workforce, said MIT's Kochan. Most workers, according to opinion polls, feel that their bosses care about them. But a strong minority do not, and have been alienated by recent trends.

"There is a broader kind of tension building up, there is a signal that we are an expendable workforce," Kochan said, "And if many people think that is how employers really view them, there will be a backlash in the workforce."

Peter Perl, an editor of The Washington Post, covered labor from 1983 through 1986.