The Civil Aeronautics Board yesterday threatened to cut back on some of Japan Air Lines' flights into the United States in retaliation for Japan's refusal to approve the planned flights of a U.S. carrier.

In a unanimous vote, the board ordered Japan Air Lines to provide the board with detailed schedules of all its flights into the United States including the frequency and days of operation of each flight, the times of arrival and departure at each point, the type of equipment used, the number of seats by class of service for each flight and the capacity of its all-cargo planes.

The action came after the Japanese Civil Aeronautics Bureau notified the United States that it would not approve these flights a week planned by Flying Tiger Lines Inc., a U.S. all-cargo carrier, between the U.S., Japan, Hong Kong, as Singapore.

Japan's action, which was formally protested by the U.S. in a diplomatic note two weeks ago, is believed to violate the air services agreement between the two countries. Although U.S. carriers are required to file their schedules with Japan for approval. Japanese carriers are not currently required to file schedules with the United States.

"Unless the Japanese government approve's Flying Tiger's schedules, the board will thereafter consider whether the operation of JAL's schedules, or any part of them, may be contrary to applicable law or adverse to the public interest, and . . . should be disapproved," the board said yesterday.

Any suspension of service would require the President's approval, but administration officials have repeatedly stated they would take the steps necessary to assure U.S. carriers fair competitive treatment abroad.

Flying Tiger had filed its planned schedules with the Japanese in November and was turned down formally on Jan. 14, a week after their flights were to be begin.

Japan's action may well be a topic of conversation at talks scheduled between the two countries later this month to take up other air matters. Another topic may be Japan's concern about Pan American World Airways' proposal to add U.S. cities to its all-cargo service from Japan. Talks on a revision of the air agreement itself are scheduled for March.

In another board action yesterday, Braniff Airways won approval to offer discounts of between 15 and 20 per cent on first-class travel beginning March 1.

Braniff plans to offer the discount on all flights in the continental U.S. when tickets are bought seven days in advance. Travelers could stay at their destination no longer than 30 days, and would be required to stay until the Sunday following the day of departure.

The 15 per cent discount will apply between June 1 and Sept. 15: the 20 per cent discount will apply all other times.