Fox Television Station Group Inc. has agreed to acquire Washington station WDCA, a UPN affiliate that is owned by Viacom Inc., the companies announced yesterday.

Fox, which already owns WTTG (Channel 5) locally, will have two stations in the Washington market after the deal closes. WDCA (Channel 20) will continue to carry UPN programming for at least two more years under a previous agreement between Fox and Viacom.

The transfer of WDCA is part of a broader deal in which Fox traded its station in San Francisco to Viacom in return for Viacom's stations in Washington and Houston.

The swap was designed to allow Viacom and Fox to own two stations in markets where they now hold one. Broadcasters have been steadily doubling their station ownership in the nation's largest cities since the Federal Communications Commission ended its ban last year on owning more than one outlet in a market. The arrangement enables them to cut costs by combining news, advertising and administrative operations.

The WDCA deal is the first such arrangement in the Washington area. If the swap is approved by the Federal Communications Commission later this year, Viacom and Fox will each own two stations in seven different cities. In addition to FCC approval, yesterday's swap is also subject to Justice Department review.

What cost savings broadcasters receive through such deals is not necessarily good news for local advertisers or audiences, said Andrew Jay Schwartzman, president and chief executive of the Media Access Project, a public interest law firm based in Washington.

Schwartzman said that broadcasters who own two stations in a market are able to squeeze advertisers by requiring them to buy spots on both stations as a condition of buying prime ad time on the stronger outlet. Audiences also suffer because it reduces the number of editorial voices in a community, Schwartzman said.

Andrew Butcher, a spokesman for News Corp., Fox Television Stations' parent company, said WDCA does not have a news operation. Butcher would not comment on any potential programming changes at WDCA, saying it was too early in the process to determine how Fox would manage the station.

Fox, which now owns stations that reach 39 percent of the country, is expected to sell four stations within the next few months. The sales will help Fox comply with an FCC rule that prohibits one company from owning stations that reach more than 35 percent of the nation's television audience.

Viacom, which also reaches 39 percent of the television audience, is awaiting the outcome of its legal challenge to the FCC rule.