BEIJING — The United States is discussing a deal with China to liberalize air travel and hopes for a framework "open skies" agreement by May, U.S. Transportation Secretary Mary Peters said Friday.

Washington hopes to produce a formal agreement by the end of this year, said Peters, who was in Beijing to discuss the possible agreement with Chinese officials.

"We want to at least have the basic framework in place by May," Peters said.

The number of airline flights between China and the United States is sharply limited by international agreement, despite rapidly rising tourist and business travel that has left aircraft packed.

U.S. carriers lobbied aggressively for one new route that was awarded this year. It went to United Airlines, which used it to launch the first direct service between Beijing and Washington last month.

Officials at American Airlines, the nation's biggest carrier, were hoping for more details Friday on just how quickly routes might be added between the two countries.

"Obviously we'd be greatly in favor of seeing more frequencies open up," said Tim Smith, a spokesman for American. "The markets between the United States and China are still greatly underserved."

American bid unsuccessfully last year for a Dallas-Beijing route. American plans to bid in the future for new flights to China, although Smith said the airline has not settled on specific routes. American is a unit of AMR Corp.

Continental Airlines Inc. supports the government's efforts to liberalize air travel between the two countries, said spokeswoman Julie King.

"Continental continues to be interested in additional flights to China, including New York to Shanghai," King said. Continental proposed a New York-Shanghai route last year, but the Transportation Department picked a rival offer by UAL Corp.'s United Airlines.

Delta Air Lines Inc. is also eager to get a foothold in China, officials at the carrier said Friday.

"Delta is keen to build our presence in Asia as a continuation of our international expansion," said spokeswoman Betsy Talton. "To this end, we've applied to provide the first and only nonstop service to China from the Southeast, and would certainly pursue additional US-China markets if negotiators agree to further liberalization."

FedEx recently obtained rights to operate 30 roundtrip flights between the U.S. and China, spokeswoman Denise Lauer said.