The Washington Post and the Detroit News announced plans yesterday to swap company-owned television stations in the two cities.

Under terms of the preliminary agreement, The Washington Post Co. would acquire NBC affiliate WWJ-TV in Detroit. In exchange, the Evening News Association, publisher of Detroit's afternoon newspaper would become the new owner of CBS affiliate WTOP-TV here.

Because the Detroit market is larger, The Post company also will pay $2 million cash as part of the exchange.

The transaction must be approved by the directors of both firms, and by the Federal Communications Commission. If approval is obtained, it would mean that The Post will no longer own any radio or television properties in Washington.

Yesterday's proposed exchange of television stations was the first involving major newspaper companies since the U.S. Court of Appeals here ruled last March that the FCC should move to force newspaper firms to divest themselves of broadcast properties in cities in which the papers are published.

That decision has been appealed to the Supreme Court by the FCC, the American Newspaper Publishers Assocation, The Washington Post Co, and other media corporations, who have contended that the court overstepped its review authority.

In 1975, the FCC had prohibited future joint ownerships of newspapers and broadcast stations in a single market but had allowed continuation of most existing ownerships. Under that FCC policy. Washington WStar chairman Joe L. Allbritton was forced to sever the Star from its local television station, WJLA-TV.

Last April Allbrition said he would exchange WJLA for an Oklahoma City station owned by Combined Communications Corp., a transaction now awaiting action by the FCC.

The Washington Post Co. also announced recently that it plans to sell radio station WTOP-AM for $6.675 million to the Outlet Co, a Providence retail and broadcast firm. In 1971. The Post company donated WTOP-FM to Howard University, which now operates that station under call letters WHUR-FM.

Washington Star Communications also has sold WMAL-AM-FM to the American Broadcasting Co, to comply with the FCC order.

In a joint announcement yesterday, Post company chairman Katharine Graham and Evening News Association president Peter B. Clark said the exchange of WWJ and WTOP would eliminate uncertained created by the still unresolved litigation over common ownership.

"Although we believe strongly that the Supreme Court should sustain the FCC's rule permitting the continuation of existing cross-ownerships, this transaction presents both companies with an opportunity to make a voluntary exchange that is mutually advantageous," the officers said in a prepared statement.

The Detroit area is the nation's seventh largest television market with an estimated 1.55 million homes that have TV sets. Metropolitan Washington is ranked eighth, with 1.37 million homes that have TVs, according to Amercian Research Bureau data for the 1976-77 TV season.

Peter A, Kizer, vice president of the Evening News broadcast division and WWJ general manager, said in a telephone interview that the Detroit market is "very competitive" with the ABC station (WXYZ) owned by that top-ranked network, a CBS affiliate (WJBK) owned by Storer Broadcasting several other commercial stations, including the nations first owned by blacks (WGPR) and a Canadian Broadcasting Corp. station in nearby Windsor, Ont.

WWJ went on the air 30 years ago as Michigan's first television station and always has been owned by the publisher of the Detroit News, long that city's dominant paper but now being challenged strongly for circulation leadership by the morning Free Press.

The Evening News Association, in business more than a century, is privately owned and controlled primarily by family members. In recent years, it has expanded through subsidiaries and now publishes newspapers in the Vineland. N.J., area and Palm Springs, Calif., and owns TV stations in Tueson, Mobile and Oklahoma City. The Detroit firm said it will continue to own radio stations WWJ AM-FM.

Joel Chaseman, president of the Post company's broadcast subsidiary, said there "appears to be a great momentum" at both stations and that no major personnel shifts are contemplated. WTOP-TV vice president James L. Snyder will move to Detroit to head up WWJ operations, Chaseman added.

Max Robinson, co-anchor of WTOP-TV's evening news program and a veteran of the station's news staff, said last night that many of his colleagues were "shocked" or "very, very angry" about the proposed exchange.

Robinson, who started work at WTOP in 1965, said he "very much regrets it coming," after a long association with Post-Newsweek stations. "I'm concerned . . . I've enjoyed working with this team . . . We get along very well . . . If I stay, it would be only with the whole group of people," he added.

Although WWJ is not the top-ranked Detroit station, it has gone "through a renaissance with a new management team" and has a strong news operation. Chaseman said.

He also said the agreement announced yesterday, after three weeks of "serious" negotiations, would have "no effect at all' on the Post company's participation in the Supreme Court media ownership case, which will be the subject of a court hearing early next year.

At stake in the ownership conflict are billions of dollars worth of broadcast properties now owned by newspaper firms in cities where they publish - 135 AM, 96 FM and 60 TV stations.

The Post company owns TV stations in Jacksonville, Miami and Hartford: Newsweek magazine, the Trenton, N.J. Times, and has investments in a Canadian newsprint company and the International Herald Tribune of Paris.

Both Clark and Graham emphasized their belief that the prospective new owners of the two television stations would maintain extensive news operations.

WTOP began telecasting in 1950. In 1954, the Post company purchased a minority interest in the station, which had been owned by the Columbia Broadcasting System.

The Detroit station has about 200 employees and WTOP employs about 180.

Kizer, who announced the planned exchange to his staff in Detroit yesterday, said they were "a little shocked" at first but "very favorable about becoming employees of The Post company.