The Washington Post DESCRIPTION: Owner of The Washington Post, Everett (Wash.) Herald, Newsweek magazine, four TV stations, interests in the International Herald Tribune, a news service and newsprint production operations (AMEX). FOUNDED: 1877. TOP EXECUTIVE: Katharine Graham, chairman and chief executive.

The Washington Post Co. pruned away its money losers last year, disposing of The Trenton Times, Inside Sports magazine and Top Market Television, an advertising sales company. Discontinuing the operations produced a $2.1 million write-off and, as a result, profits were down for the second year in a row, to $32.7 million from $34.3 million. The company's three principal divisions each produced record revenues, with newspapers up 18 percent, magazines up 10 percent and broadcasting up 13 percent. Concentration of the company's resources in those divisions "has put them in an unusually strong position to take advantage of the opportunities that will emerge in the rapidly changing media marketplace of the 1980s," Chairman Graham told shareholders.

Richard D. Simmons, formerly vice chairman of Dun & Bradstreet, became president of The Post Co. in September. The death of The Washington Star produced a surge in circulation for The Post, but paradoxically also cut into profits because advertising revenues did not rise fast enough to keep up with the cost of printing the extra papers. With daily circulation up 23 percent to 771,000 and Sunday distribution up 17 percent to 984,000, The Washington Post now ranks sixth in weekday circulation and fifth among Sunday papers.

Communications Satellite Corp. (Comsat) DESCRIPTION: Comsat and a subsidiary, Comsat General Corp., are engaged primarily in providing international, maritime and U.S. domestic communications satellite services. Another subsidiary, Environmental Research & Technology, provides consulting, planning and computer-based information services (NYSE, M, P, Phila.). FOUNDED: 1963. TOP EXECUTIVES: John D. Harper, chairman; Joseph V. Charyk, president and chief executive officer.

Communications Satellite Corp. is investing heavily in the future, betting on raising its visibility in the business and consumer communications market by taking advantage of federal procompetitive telecommunications policies and jumping into two dramatic new ventures.

That commitment shows on the bottom line as the company reported that profits, excluding an accounting policy change, fell to $28.3 million last year, down about $10 million or $1.25 a share from 1980. Most of that loss was attributed to the company's growing investment in Satellite Business Systems, the joint venture with International Business Machines Corp. and Aetna Life & Casualty that itself is one of Washington's Top 100 companies.

Comsat so far is incurring only legal fees for its second new field, television programming and marketing. If the company gets government approval for the service, it is prepared to invest directly $225 million in a subsidiary, Satellite Television Corp., which will attempt to offer the first direct broadcast satellite (DBS) service to homes.

Comsat is also diversifying away from its more traditional international satellite services and into manufacturing, completing in 1981 the largest acquisition in its 20-year history, a $57 million purchase of Amplica Inc., a California microwave equipment company.

MCI Communications Corp. DESCRIPTION: Specialized telecommunications common carrier, based in Washington, which owns and operates the second-largest common carrier radio network. Built at a cost of more than $200 million, MCI's network serves 76 major metropolitan areas with 3,500 communities and more than 60 percent of the U.S. telephones. The D.C. firm competes with American Telephone & Telegraph in providing long-distance services but does not manufacture equipment or offer local telephone exchange service. Business telephone service is MCI's major market (OTC). FOUNDED: 1968. TOP EXECUTIVES: William McGowan, chairman; V. Orville Wright, president.

MCI Communications Corp. has helped to create one of the glamour businesses of the 1980s--competitive long distance telecommunications.

The company, which only a half dozen years ago was on the verge of bankruptcy, last year moved to its own building, plush new quarters on 19th St. NW, and is expected to become one of the largest companies in business history to double its sales in one year when, as analysts have predicted, it announces next month 1982 fiscal year revenues of more than $500 million.

Profits for the company's third quarter jumped to $26.6 million, more than the $21.1 million in earnings MCI reported for all of 1981, and for the nine-month period, profits rose from $13.1 million in 1981 to $52.6 million in fiscal 1982.

The secret apparently is aggressive marketing and sharp lawyers, who still await an appeals court judgment on MCI's successful antitrust suit against American Telephone & Telegraph Co. A jury awarded MCI $1.8 billion, apparently the largest verdict of its kind in history.

Another judicial action, the proposed settlement of the government's antitrust suit against AT&T and the planned break-up of the Bell System also appears to bode well for MCI, which had argued aggressively for a break-up along the lines of the pact. As a result of the settlement, MCI expects to gain equal access to local telephone networks, a source of regulatory and judicial debate since MCI went into business in the early 1970s.

In addition to developing its cut-rate long distance telephone business, MCI also moved into two new ventures last year. It expanded into international communications fields by buying Western Union International Inc. from Xerox Corp. for about $185 million. That deal is expected to be completed by midsummer. MCI also plans to spend $40 million on its own domestic data business, one facet of a capital expansion program that is running at a cost of about $1 million a day.