Communications Satellite Corp. (Comsat) yesterday announced plans to begin operating a two-channel pay television service in late 1983.

The announcement indicates that Comsat is ready to get directly into the television business for the first time, well before the 1986 date when the company hopes to begin providing the nation's first Direct Broadcast Satellite (DBS) service.

The pay television service is designed for apartment and condominium buildings, as well as hotels and mobile home parks, but will be available only in the northeast. Like the nationwide three-channel direct-to-home DBS service already proposed to the Federal Communications Commission, the newly announced pay TV programming service requires FCC approval.

Comsat became the first American company to formally propose DBS service last year. Under the plan, subscribers would have installed at their homes Comsat receiving antennas which could receive three television channels beamed directly from orbiting satellites.

The company has said that after FCC approval it could take as long as 3 1/2 years to introduce the full-scale service, and yesterday's announcement speeds the possibility of Comsat's entrance into network television through a wholly owned year-old subsidiary, Satellite Television Corp. (STC).

Since that application was filed late last year, however, other firms, including RCA Corp. and CBS Inc., have also proposed introduction of the direct-to-home service. The FCC is currently reviewing the applications and working to assemble regulatory standards for the service. Speedy approval of the venture has been opposed by some broadcasting interests.

Under the new plan, the signals would be distributed to subscribers through a master antenna system. One channel would offer 24-hour-a-day motion pictures, while the second would provide 15 hours daily of films, sports and variety shows. In the announcement, Comsat said subscribers will pay installation charges and a fully refundable deposit when the service is introduced.

Beyond regulatory approval, however, Comsat has been attempting to find a partner to serve as a supplier of equipment, such as the antennas and decoders to unscramble the signals. Talks last year with Sears, Roebuck & Co. were unsuccessful.

The company said that when STC introduces the three-channel service, subscribers to the two-channel system will be switched to DBS, which will offer such options as stereo sound and a broader range of programming.