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By David Morgan

WASHINGTON, Feb 3 (Reuters) - Republicans in the U.S. House of Representatives on Wednesday introduced a measure to privatize the national air traffic control system by placing it in the hands of a new private nonprofit corporation run by airlines and other stakeholders.

The long-anticipated measure would transfer air traffic operations and 38,000 government employees from the Federal Aviation Administration to the nonprofit, in a bid to reduce flight delays, speed the adoption of next-generation technology and insulate the system's funding from congressional gridlock.

But Democrats and other critics warned that the move could lead to a costlier, less-efficient system controlled by the airline industry. They vowed to unveil a rival plan for targeted reform that would protect air traffic control from congressional politics by making its funding mandatory.

"Our system is incredibly inefficient, and it will only get worse as passenger levels grow and as the FAA falls further behind in modernizing the system," said U.S. Representative Bill Shuster, a Pennsylvania Republican who chairs the House Transportation and Infrastructure Committee.

Shuster, who expects to send the legislation to the floor of the House next week for a possible vote, said the plan is modeled on private air traffic control operations in other countries, including Canada and Britain.

The bill won ready backing from the Airlines For America, a leading industry trade group, and the main air traffic controllers union.

But its future was unclear ahead of the November election, when voters will determine which party controls the White House and Congress in 2017.

"We cannot support the proposal," said Representative Peter DeFazio of Oregon, the committee's top Democrat, who said he was concerned about whether it would meet acceptable safety, national security and public interest standards.

Unionized commercial pilots also objected to the measure. Delta Air Lines Inc has already warned that it would lead to higher costs for passengers.

Republicans anticipate a three-year transition from government to private control under the proposal. It is expected to reduce annual federal FAA spending from $14 billion to $3 billion, aides said. Lost tax revenue would be replaced by user fees. But those details have yet to be worked out by the House Ways and Means Committee, which has jurisdiction over taxes.

Republicans said privatization is necessary to ensure greater efficiency and modernization, pointing to a recent Transportation Department report saying two decades of reform have failed to make the FAA more efficient.

(Reporting by David Morgan; Editing by Chizu Nomiyama, Grant McCool and Jonathan Oatis)