The proposed sale of WDCA-TV (Channel 20) to Chicago's Tribune Co. was cancelled yesterday.

And the fate of the largest broadcast sale in history -- the proposed exchange of WJLA-TV (Channel 7) for KOCO-TV in Oklahoma City -- rested with Washington Star Communications Chairman Joe L. Allbritton, who must decide whether to extend a contract that expires today.

The Tribune Co., owner of the Chicago Tribune and New York Daily News, said it agreed to "terminate discussions" with Channel 20's owner, Superior Tube Co., on Wynnewood, Pa.

An official statement by spokesmen of the two firms said only that they were unable to reach final agreement on financial terms of the sale. Tribune Co. had agreed to buy WDCA, an independent station that would complement its TV operations in New York and Chicago, for a reported $12 million in January.

But broadcast industry sources said last night that following the distribution of new TV ratings for January and early February, showing a sharp increase in Channel 20 viewers, Superior Tube sought more money for the property.The Pennsylvania firm bought WDCA in 1969 for $4.8 million from the station's general manager, Milton Grant.

Recent Arbitron ratings, according to a station official, showed a broad increase in early evening and weekend ratings. For example, the station's 1-3 p.m. Sunday movie topped all area network affiliates with women viewers up 346 percent and men viewers up 522 percent in January over last year.

As for the proposed sale of WJLA, owned by Washington Star Communications, company owner Allbritton faces for the second time in a week a decision on whether to extend a purchase contract.

The Federal Communications Commission now plans to decide next Wednesday whether it will approve the swap of WJLA for the Oklahoma Corp., of Phoenix, which owns KOCO-TV.

Although the regulatory agency approved the deal in January, principally to aid the Washington Star newspaper with revenues from the swap, a recondieration was ordered after Allbritton agreed to sell the newspaper to Time Inc. Four citizens groups who oppose the sale have asked the FCC to hold public hearings again before taking final action.

Under terms of the original Allbritton-Combined agreement, it was to expire at the end of February without final FCC action. When the FCC earlier said it would decide this week, the two companies extended their contract through today.

Combined Communications chief counsel Lawrence R. Wilson said last night his firm is willing to extend once more and that the decision is up to Allbritton. The star chairman was reported to be studying his options last night.