The Civil Aeronautics Board yesterday rejected a request that it decide by Sept. 15 whether to permit the government of China and Pan American World Airways to operate the first nonstop passenger flights from the United States to China in 30 years.

In an application filed Aug. 16, Pan Am and China asked the board to speed up its procedures to meet the Sept. 15 date because after that date either party can withdraw from their agreement setting up the flights. The pact calls for Pan Am to operate three roundtrip charter flights from San Francisco to Shanghai for China and its airline and for Pan Am to operate three more of its own. The first flight is schedule to depart San Francisco on Dec. 17.

In turning down the request to expedite its process, the board said the application is too important to be rushed," This is a novel case of obvious significance to the public and the air transportation industry," it said.

It expressed special concern that it have assurances that charter air service between the United States and China by other interested U.S. airlines will be possible, "We are concerned that this proposal not confer on Pan American a preferred position that would harm the interests both of other U.S. carriers seeking entry into the United States-China market, and of the traveling public," the board order says.

A half-dozen airlines have asked the CAB for authority to fly to China should a bilateral air services agreement be reached. The board's order -- issued under delegated authority by Sandford Rederer, director of the bureau of international aviation, and Barbara A. Clark, director of the bureau of domestic aviation -- doesn't mean a lengthy delay in consideration of the application. The order gives interested persons until Sept. 6 to comment on the application, and gives Pan Am and China until Spet. 20 to reply to the comments.

The board also asked the State Department to solicit from the appropriate governmental bodies of the People's Republic of China information responsive to the concerns raised in the order.

A spokesman from Pan Am said last night the company could not comment on the board order because it had not yet seen a copy of it.

Under the Pan Am-China agreement, China will lease Boeing 747SPs for the flights operated on its behalf, and Pan Am will provide cockpit crews. The Chinese have ordered several 747SPs and the proposed flights are designed in part to familiarize the Chinese with the plane.