A federal appeals court yesterday overturned one of the biggest union organizing victories of the decade, nullifying the 1997 representation election of 10,000 passenger reservation agents at US Airways Inc.

The decision comes as the Arlington-based airline and the Communications Workers of America were reported near agreement on a new contract for a work force that has had its wages frozen since 1990.

The ruling also could mean that the passenger reservations agents, who have not had a wage increase since 1990, could face months or even years before they get any more money if the ruling is appealed or the company refuses to recognize the union. Under federal labor law, an employer cannot unilaterally increase compensation during an organizing campaign or contract talks.

A three-judge panel ruled that a lower court was wrong when it concluded that the airline's management had coerced company employees during a CWA organizing drive in 1996. The court's ruling nullified the results of an election in early 1997, which the union lost, and set the stage later that year for a rerun election, which the union won. In effect, yesterday's ruling restored the results of the first election.

The CWA lost the January 1997 representation election, even though the vote was 3,973 for the union, 200 for other unions and 200 challenged ballots. Under the National Railway Labor Act, which governs airline industry labor relations, a union not only has to win a majority of the votes, but a majority of the eligible voters must have participated in the election. There were 9,272 eligible voters at the time.

The union appealed the election results to the National Mediation Board, which supervises elections in the industry, and won. The board ordered a new election and the lower court upheld the ruling. The CWA then won the rerun election with a 54 percent majority of eligible voters.

At the time, the CWA victory represented the biggest representation victory for organized labor in more than a decade. It was cited by top leaders of the AFL-CIO as the beginning of a comeback for the trade union movement after years of membership decline.

US Airways would not comment yesterday on the decision. In a brief statement to company employees, Michelle Bryan, senior vice president of human resources, did not say how the ruling might effect current negotiations. "In light of the importance of this matter to all of us, we will keep you fully informed regarding all additional developments," Bryan said.

The CWA vowed to continue bargaining for its first contract with the airline. In a statement, the union said it "is very close to completing negotiations for that contract."

At the US Airways annual meeting in Charlotte last week, Chairman Stephen M. Wolf acknowledged that the reservations agents had gone a long time without a wage increase or paid time off and that he hoped the company soon would be able to reach agreement on a new contract with the CWA.

The union said it would pursue "any legal and procedural steps necessary to bring this contract to a conclusion."

The National Mediation Board and the union can appeal yesterday's decision, but yesterday neither indicated their intentions.