WASHINGTON (AP) _ The Gannett Co. will sell television stations in Oklahoma City, Okla., Mobile, Ala., and Tucson, Ariz., to Knight-Ridder Newspapers, it was announced Friday.

The sale is required by Federal Communications Commission rules as a consequence of Gannett's purchase of the Detroit Evening News Association. The commission prohibits a single owner to have a newspaper and television station in the same market.

The acquisition of the Evening News and its newspapers and broadcast stations in Michigan, California, Texas, New Jersey and Washington, D.C., creates a number of prohibited cross-ownerships for Gannett.

Knight-Ridder will pay $160 million for KTVY-TV, an NBC affiliate in Oklahoma City; WALA-TV, an NBC affiliate in Mobile; and CBS affiliate KOLD-TV in Phoenix.

In the statement announcing the sale, Gannett said it would move its broadcast division headquarters from Atlanta to Washington.

Gannett also promised to announce ''soon'' a buyer for two Detroit radio stations it must sell.