Rep. Eugene V. Atkinson, sitting knee to knee with his Democratic rival, Joe Kolter, for a debate at radio station WBVP, said with a certain bravado, "Maybe I will pay a political price, maybe I won't."

Atkinson was referring to his conversion to Republicanism, an event solemnized in the Rose Garden just a year ago today. It seemed like a good idea at the time. Ronald Reagan was riding high, and steel mills in Beaver County, second most populous county in the newly drawn 4th Congressional District, were operating at 82 percent of capacity.

Today, Beaver Valley is blighted with joblessness. The rate is 20.5 percent. This week Crucible Steel, which once employed 9,000 workers, will close. And the embittered and newly galvanzed labor unions are rallying to make Atkinson, who claims he was hopelessly attracted to Reagan because of his deregulation policies, pay the price for what they call his "betrayal."

Says a steelworker in the Union Hall of Local 1082 who was laid off from Babcock & Wilcox Co. a month ago: "Atkinson was one of our brothers, and he should have stayed right with us. He betrayed us when he switched."

On Beaver Falls' main street, a guard at the entrance of a Republic Steel subsidiary, where the work force has been cut by two thirds, says of Atkinson: "I never did like him. He talks out of both sides of his mouth. The switcheroo was a big factor."

The guard spoke the reservations, which elsewhere are either translated or suppressed, about Democrat Kolter, a 14-year veteran of the legislature: "He's a good man and a good family man, but I wouldn't give two bits for him as a congressman. He has just been a messenger boy in Harrisburg. I want somebody who will do something big for the people."

The guard, a John B. Anderson voter in 1980, may go for the third-party man in the race, Sam Blancato of the Citizens Consumer Party. He was included in the radio debate and provided an obligato of mutters of "insanity" about Reagan's attitudes on defense, corporations and nuclear weaponry.

Danny Sisco, in sandals, put his head inside the guardhouse to submit a form for supplementary unemployment benefits. Laid off seven months ago, he had just taken his younger child to nursery school. He is "following" Kolter -- "you can't trust Atkinson, I guess, because he switched."

The Atkinson-Kolter contest is attracting national attention and prominent visitors. House Speaker Thomas P. (Tip) O'Neill Jr. (D-Mass.) is coming in next week to castigate the turncoat. Former vice president Walter F. Mondale and Sen. John Glenn (D-Ohio) preceded him.

Vice President Bush did a fund-raiser for Atkinson, and Pennsylvania's Republican stars -- Health and Human Services Secretary Richard S. Schweiker and Transportation Secretary Drew Lewis -- are due in to boost their new brother.

Atkinson is a small, nimble-witted Irishman, with a history of political impulsiveness: he backed Sen. Edward M. Kennedy (D-Mass.) in 1980. He is a fluent speaker. At one point, he said, with some justice, to Kolter, "You are not knowledgeable."

Kolter, a large gray-haired man, speaks slowly and laboriously. He read everything during the debate. Opening remarks, closing remarks, even jibes and asides were carefully typed out. He was so chained to his script that one could almost hear the rattle of manacles when he moved. The sound of turning pages was clearly audible.

His bright young campaign manager, Jerry Weaver, has no apologies.

"Look," he says of his principal, "he spent 14 years in Harrisburg. He has no experience in national or international affairs."

Weaver had given Kolter some good licks. "You should have asked the president for steel quotas instead of a quarter of a million dollars in campaign funds, when you were in the Rose Garden."

But Atkinson's spending, which one campaign aide said could be in excess of $500,000, is not an issue here. And the steelworkers could not care if Kolter spoke in his ancestral Croatian. The only question here is unemployment.

"People are not going to vote their party affiliations," according to Atkinson. A few minutes at Local 1082 would disabuse him of that fancy.

Says union President Thomas Berger: "Reagan has succeeded in bringing us together again. The labor movement got off its duffs. We were dormant. We got caught with our pants down, and Reagan hit us between the eyes."

With nothing else to do, laid-off steelworkers, having helped register voters at grocery stores and unemployment offices, are handing out Kolter literature, manning telephone banks and upping their election day pullout forces from 20 to 100 workers.

"Joe Kolter is one of us," says John Todorich, loud-voiced chief of the local's benefits branch. "Gene Atkinson don't stand for anything but himself."

What he stands for now in the eyes of this depressed valley is Reaganomics gone sour, a turncoat with a bad sense of timing.