WASHINGTON — Supporters of the merger of Delta and Northwest airlines are working both their inside and outside games, as company executives and labor union leaders head to Capitol Hill Wednesday to testify on how the deal would affect America's troubled aviation industry.

The congressional hearing, the third on the merger, comes as Delta has reinforced its lobbying team with some of the best-known firms on Washington's K Street.

The merger also is getting help from advocacy groups, including from an unexpected quarter. The Consumer Federation of America, which typically lobbies hard against big business, is preparing to endorse the merger at today's hearing before the Senate Commerce Committee's aviation subcommittee.

Mark Cooper, the federation's director of research, said he would testify in favor of the proposal to create the world's largest air carrier because the current condition of aviation is so dismal.

"If you think about the prospects of opposing the merger and saying we want to keep the industry the way it is — well, it stinks," he said. "The industry pleases no one. Consumers hate it, labor hates it, investors hate it."

Cooper said the merger proposal is "an admission of a fundamental failure" of the deregulation of airlines. He said Congress should not try to block the deal but should pass federal laws and rules to protect passengers' rights.

In a news release that called the merger "pro-consumer," Robert K. Johnson, president of Consumers for Competitive Choice, said the combined new airline would have "the resources and might to weather the difficulties that have plagued other airlines."

Washington-based Citizen Outreach fired off an e-mail to 25,000 supporters nationwide saying the Delta-Northwest combination would mean more stability for airlines. The head of the group, Chuck Muth, said that he would monitor the merger's progress and launch a "grass-roots" effort if the deal runs into trouble as it seeks approval from the Justice Department's antitrust division.

Citizen Outreach and Consumers for Competitive Choice both receive backing from the business community, but they denied receiving funds from Delta or Northwest.

The airline merger continued to face opposition from labor unions, including the International Association of Machinists and Aerospace Workers, which represents Northwest employees. A union official was scheduled to address the Senate hearing Wednesday.