Newport News Shipbuilding and Dry Dock Co., Virginia's largest private employer, abruptly acquesced to a federal court order yesterday and recognized the United Steelworkers Union of America as the legitimate bargaining agent for its 15,500 bluecollar workers.

Abandoning a long fight to keep the national union out of the huge shipyard, the company announced it will not appeal an appeals court ruling issued Thursday that upheld the Steelworkers as the winner of a bitter union representation election.

The company's decision -- which represents a major breakthrough in organized labor's long campaign to organize the historically non-union South -- was hailed by hundreds of jubilant workers who marched past the yard in celebration yesterday.

The shipyard had refused to bargain with the Steelworkers, contending that its Jan. 31, 1978, union representation victory over the unaffiliated -- and company-backed -- incumbent Peninsula Shipbuilders' Association was tainted by voting fraud.

A 13-week strike by the Steelworkers earlier this year failed to bring the company to the negotiating table and was suspended after up to 75 percent of the production and maintenance workers returned to their jobs.

The strike's end in mid-April was considered by many labor observers a setback in the AFL-CIO's often frustrated efforts to make inroads in the South, a region with many right-to-work laws that prohibit mandatory union membership. But Steelworkers officials said yesterday they had pinned their hopes all along on the court ruling and its eventual acceptance by shipyard management.

"We're disappointed that the 4th Circuit (Court of Appeals) did not agree with our arguments and are still convinced that the representation election was flawed by serious voting irregularities," said Edward J. Campbell, company president, in announcing that the shipyard would soon enter contract negotiations with the Steelworkers.

Though the company official had promised months ago to abide by the appeals court's decision, Campbell's announcement yesterday came as a surprise to the union, which has watched other large southern employers wage protracted court battles to keep unions out of their plants.

"We're encouraged by Mr. Campbell's statement and believe we can now begin to bargain an honorable contract for our members," said Jack Hower, a Steelworkers subdistrict director in Newport News.

Shipyard union members, estimated to account for 12,000 to 13,000 of the yard's blue-collar work force of 15,500, were "very jubilant and happy a final decision has come down," Hower said. He said could not predict how soon Steelworkers representatives would actually begin negotiations with the shipyard.

The Steelworkers struck the shipyard, a subsidiary of the Houston-based Tenneco Inc., conglomerate, on Jan. 31, the first anniversary of the union's representation victory. The National Labor Relations Board had certified the union as the winner, with 9,093 votes over 7,548 for the rival independent Peninsula Shipbuilders association.

Even though the strike was generally perceived as having fizzled, Steelworkers and their supporters insisted yesterday that the labor action had hastened an ultimate victory for the union by speeding up court consideration of the representation case.

"The sole purpose of the strike was to expedite the legal process," said Elmer Chatak, a former organizing director for the union who recently became secretary-treasurer of the AFL-CIO's Industrial Union Department.

The shipyard's original appeal challenging the representation election "could have taken three or four years if the union had opted to let the company run out the legal process," Chatak said.

And the Newport News strike itself, Chatak argued, would have garnered more worker support if it had been called over economic issues. "Workers aren't accustomed to striking over union representation," he said.

Shipyard spokesman Jim Griffith complained yesterday that the Steelworkers had called the strike to force the company "to give up our right to our day in court.

"But we wanted an independent review of the representation election, which we didn't feel was possible with the NLRB," he said. "We were satisfied with the opportunity to take this to court."

Griffith said that unlike "other instances where companies take every possible means to drag it out, that was not our objective."

Virginia Gov. John N. Dalton ordered state troopers to Newport News at the onset of the strike so that workers who wanted to work could be protected as they crossed picket lines.

Only the federal government is a larger employer in Virginia than the company, which buys $77 million a year in goods and services from other Virginia firms, pays$430 million a year in wages and benefits and accounts for $17 million a year in state and local taxes.

Union officials cited yesterday's shipyard announcement as a needed boost for other organizing efforts in the Sunbelt, particularly the Steelworker's efforts to organize large employers such as DuPont.