Ron Weisen, president of United Steelworkers Local 1397 here, has a theory about the company that has employed and the union that has represented him for 28 years.

The company, United States Steel Corp., and the union are trying to get out of the steel business, Weisen said.

"We've become a minority in our own union," said Weisen, referring to the remaining 350,000 steelworkers among the union's estimated 1.2 million members. "The union's gone after white-collar workers in offices and other places to broaden its dues base, and the company's gone into the oil and chemical businesses to get more profits," he said.

To counter what he sees as "a movement to abandon the steelworkers," Weisen has taken his union and U.S. Steel to court and has peppered both with insults in his nationally circulated newpaper, "1397 Rank & File." He has led demonstrations at U.S. Steel's century-old Homestead Works plant here and at corporate and union headquarters in nearby downtown Pittsburgh. And he has started a drive to give each union member the right to vote on collective bargaining agreements. Under the current system, only local union presidents are allowed to vote on contracts.

Weisen has also gone into the community action business. His local has staged a rock concert and other events to raise money for unemployed steelworkers here and in adjacent communities. The local also runs a food bank that feeds several thousand needy families every month.

The upshot has been an surge in popularity for Weisen that could help him win the union's District 15 director's race next July-a victory that would place him on the international union's 30-member executive board. The USW board is more powerful than similar policy-setting bodies in other unions, largely because of its virtual independence from the steelworkers' biennial constitutional convention.

As a result, some USW and U.S. Steel officials fear that Weisen could increase his capacity for mischief as a board member enough, perhaps, to cause trouble in scheduled 1983 industry, bargaining.

"Right now, Weisen is more bark than bite in his dealings with the company," one knowledgeable Homestead Works official said. "But we're all concerned that he could be a detriment to negotiations" if he found a place on the board, the official said.

A high international USW official, who asked not to be identified, said "Weisen is a media-crazy wild man, but he has a stable of writers working for him that make him look good to some members of the rank-and-file. He ahs people coing from far and wide to work for him, trying to turn him into another Sadlowski."

The reference was to Edward Sadlowski Jr., a dissident Chicago USW district director who unsuccessfully challenged USW President Lloyd McBride for leadership of the international union in 1977. McBride beat Sadlowski by 80,000 votes. But the race left a legacy of bitterness toward the international that, in the current enviroment of increased layoffs and plant closings, seems ripe for exploitation. Weisen, a 46-year old former boxer and self-avowed populist, said he has every intention of taking advantage of the situation.

"The international is too busy diversifying its base to do anything for the steelworkers. . .They're in bed with the corporation down there in Pittsburgh. The international offficers are in bed with the corporation so much they ought to file for maternity benefits," Weisen said, using a line that has won him laughts and applause on numerous occasions. But his specific charges are not so funny -not to the targets of his ire, nor to the workers he says his local is fighting to represent.

Weisen said the international did little to try to stop U.S. Steel from investing $6 billion in the acquisition of Marathon Oil, a deal completed March 11. With nearly 90,000 basic steelworkers on indefinite and temporary layoff, with aging plants like Homestead badly in need of capital improvements to keep functioning, "the money would have been better spent on putting in new machines to keep plants going and people working," Weisen said.

U.S. Steel, the nation's largest steelmaker with 22 domestic steel products facilities, "could have modernized every one of its steel plants in the country with the $6 billion it spent on Marathon," Weisen said.

Operating under that belief, Local 1397 last year filed two lawsuits against the company seeking disclosure of any plans for plant improvements or shutdowns. The local "has another injuction ready to go" if, as many here expect, U.S. Steel proceeds with plans to close another production unit, Open Hearth No. 5, at its Homestead plant, Weisen said.

Homestead employed nearly 7,000 Local 1397 members in 1980. But that figure has fallen to 4,000 actively employed unionrepresented worrkers today, according to the local's records. Weisen and his supporters have gone to court with charges that the international has failed to protect its members in plant closings and other matters, and that the union hierarchy has, in effect, engaged in a kind of taxation without representation.

"The international takes 60 percent of the dues we collect each month. We figure that we ought to get something for our money," said David Horgan, 39, a Weisen lieutenant who has worked at Homestead for 18 years. Horgan said the layoffs, plant closings and alleged inaction by the international has put rank-and-file steelworkers here and elsewhere in a rebellious mood. He said that mood will manifest itselt if industry negotiators come to the union next year, or earlier, in search of wage and benefits concessions.

That attitude contrasts with those of industry and union leaders, who say that some compromises will have to be made to help companies like National Steel Corp., the nation's fourth-largest steel producer, which lost $40.2 million in the first quarter of 1982. Third-ranked Bethlehem Steel lost $66.7 million during the same period. U.S. Steel reported a net income of $79.9 million for the first quarter, down 71 percent from the $270.9 million the company earned in the first quarter of last year.

Weisen, who at the moment is facing five other opponents for the District 15 seat, remains unimpressed by the figures. He even wants the union and industry to eliminate permanently the Experimental Negotiating Agreement, under which the two parties negotiated no-strike contracts in 1974 and 1977. The agreement was set aside in 1980, pending review by union and management bargainers.

"We had a strong union when we had the right to strike. But the union has gone backwards since we gave up the right," Weisen said, adding that "having the right to strike doesn't mean we have to use it."

Still, that kind of talk upsets industry and union negotiators who, since last Oct. 1, have been studying the possibility of using the agreement as the basis for 1983 talks. In the past, USW officials such as Vice President Joseph Odorcich, have taken Weisen aside and asked him to dampen his rhetoric and stop his demonstrations.

But Weisen has responded by using his newspaper to ridicule Odorcich and others as being among "McBride's harem of cronies. . . who talk loud about freedom and dignity for workers while they ruthlessly deny their membership any of the basic freedoms. . ."

So, the USW leaders have changed their approach in favor of, they hope, letting Weisen burn himself out "by running against Pittsburgh," one ranking union official said. "Everybody who has been in office in that local has always been against whoever was in office in Pittsburgh," the official said. "Weisen isn't the first. He just has more media savvy than a lot of his predecessors."