Entertainment: Comsat Corp., a Washington-based satellite communications company, has agreed to buy Los Angeles-based film and television producer Beacon Communications. Beacon, owned by Armyan Bernstein, Marc Abraham and Tom Rosenberg, produced the 1991 critical hit "The Commitments," as well as the upcoming Columbia Pictures release "The Road to Wellville." Bernstein and Abraham will remain with the company after the purchase is completed. Comsat will pay $10 million in cash for Beacon's assets and will assume $19 million in liabilities, plus "future cash consideration" based on Beacon's performance over the next five years. Beacon has a production financing and distribution agreement with Sony Pictures. Creative Artists Agency, Allen & Co. and Salomon Bros. advised Comsat on the acquisition. Comsat also said it signed a memorandum of understanding to build a 19,000-seat sports and entertainment arena in Denver, set to open in 1997 or 1998, in joint partnership with Anshutz Corp. Comsat owns the Denver Nuggets basketball team.