The Washington Post Co. yesterday reported first-quarter earnings fell to $12.4 million (96 cents a share) from $13.9 million (99 cents) a year ago, primarily the result of refinancing part of the debt connected with the purchase of its cable-television operation earlier this year.

In other media company earnings reports, Tribune Co. and New York Times Co. yesterday posted higher first-quarter net income, while A. H. Belo Corp., Knight Ridder Newspapers Inc. and Capital Cities-ABC Inc. reported declines in first-quarter profits.

The Washington Post Co.'s first-quarter earnings in 1985 were actually $24.9 million ($1.78 a share), but that figure included after-tax gains of $11 million (79 cents) from the sale of portions of the company's SportsChannel and cellular telephone interests.

Revenue for the three months grew to $276.8 million from $243.6 million and operating income was up 45 percent to $37.3 million from $25.8 million. Excluding results from the cable-TV systems acquired within the last year, operating income grew 38 percent, the company said.

The Post Co. said this year's first-quarter earnings were reduced $2.2 million by charges for refinancing $98.6 million of debt. The company purchased 53 cable systems from Capital Cities Communications in January for $350 million.

This was somewhat offset by an increase of $1 million as the result of a change in accounting rules for employe pensions. The change in pension accounting will add about $4 million to reported earnings this year and the refinancing will save about $1 million a year, the company said.

The company's newspaper division, which produces The Washington Post and The Everett (Wash.) Herald, reported a 3.6 percent increase in revenue, despite a 1 percent decline in advertising inches at The Post, to 1,258,000 from 1,272,000.

Newsweek revenue rose 7 percent, and the magazine published two more pages of domestic advertising (550 versus 548) than in the same period a year ago. Revenue of Post-Newsweek TV stations was up 8 percent and the new cable division produced $20 million in revenue. Revenue from other businesses was up 13 percent. The company's equity in earnings of affiliates grew to $1.9 million from $148,000 because of substantially lower losses at SportsChannel and improved results from the company's newsprint affiliates.

*Tribune Co., a diversified media company, said its net income, excluding gains from its sale of the Los Angeles Daily News, was $18.3 million (45 cents a share). Including income from the $176 million sale, Tribune Co. posted a first-quarter profit of $106.9 million ($2.63).

First-quarter profits last year were $16.6 million (41 cents).

Properties of Tribune Co. include the Chicago Tribune and New York Daily News newspapers, television stations KTLA in Los Angeles, WGN in Chicago and WPIX in New York, the Chicago Cubs baseball team and newsprint and paper manufacturing operations.

Tribune Co. said its first-quarter operating revenue rose to $453.5 million from $449.4 million last year, despite a 2 percent drop in newspaper publishing revenue.

Profits in the newspaper unit, which publishes the Chicago Tribune and New York Daily News, increased by 22 percent, and earnings rose in the company's newsprint and forest products division. Tribune Co. also reported a slight increase in losses for its broadcasting, entertainment and cable television division, primarily from non-cash expenses in acquiring KTLA.

*New York Times Co. posted first-quarter profits of $33.9 million (84 cents a share), compared with $32.3 million (81 cents) a year earlier. The media company reported first-quarter revenue rose to $375 million in 1986 from $328 million last year.

First-quarter 1985 earnings included the one-time net gain of $2.8 million from the sale of property in New York.

Chairman Arthur Ochs Sulzberger said earnings were diluted by interest expenses stemming from the acquisition of five newspapers and two television stations during the final three quarters of 1985.

Times Co. said operating profits rose 22 percent for the New York Times and 33 regional newspapers; 50 percent for its magazine group; and 62.5 percent for its broadcasting and cable television unit.

*A. H. Belo, owner of the Dallas Morning News, reported net income of $1.6 million (14 cents a share), in the first three months of this year, compared with net income of $2.4 million (21 cents) in the same period of 1985.

The company said first-quarter revenue increased to $90.2 million from $85.7 million a year earlier.

Belo attributed the sharp drop in profits to higher costs stemming from increased circulation, larger depreciation expenses and higher television programming costs.

Belo also publishes a chain of suburban newspapers and is the owner-operator of five network-affiliated television stations and of radio stations in Dallas and Denver.

*Knight-Ridder posted net income of $26.6 million (46 cents a share), in the first quarter, down from $28.9 million (44 cents) a year earlier. Total operating revenue rose to $447.3 million from $421.8 million.

In a news release, the company attributed the profit decline to costs stemming from the $160 million purchase of three television stations in February and a major repurchase of the company's stock. Knight-Ridder also said one-time costs from the shutdown of its Viewtron videotext service in March lowered first-quarter earnings by two cents a share.

Knight-Ridder newspapers include the Miami Herald, Philadelphia Inquirer and Daily News and the Detroit Free Press. The company also owns eight television stations.

*Capital Cities-ABC reported first-quarter net income of $1.97 million (12 cents a share), not including a one-time gain of $279.9 million from the sale of three television stations, its cable-television system and three radio stations.

Including the one-time gain, first-quarter profits totaled $281.9 million ($17.48). Net income for the first quarter of last year was $27.74 million ($2.13).

The properties were sold in conjunction with the merger of Capital Cities with American Broadcasting Companies Inc., which was completed on Jan. 3.

Net revenue, including ABC, totaled $912.3 million in the first quarter, compared with $234.1 million a year earlier.

Capital Cities-ABC said the first quarter was adversely affected by weak network advertising demand and a declining audience share for the ABC Television network, but "all other operations met or exceeded expectations."