The Reagan administration has strongly endorsed efforts by Communications Satellite Corp, to launch the nation's first direct satellite-to-home broadcasting service.

In a letter last week to the Federal Communications Commission, Commerce Secretary Malcolm Baldrige urged the FCC to " act promptly" to resolve the regulatory policy questions that surround the Comsat application for the new service.

"The commission has been a leader in promoting free market competition and deregulation in telecommunications over the past decade," Baldrige wrote in a letter to acting FCC chairman Robert E. Lee.

"The administration strongly supports these goals. DBS [direct broadcast satellites] has the potential to bring valuable new services to the television marketplace, to advance U.S. technology in satellite communications and to create new jobs while providing our equipment manufacturers with both new domestic and international markets.

"Government cannot insure that these benefits will be forthcoming, but it should not place unnecessary obstacles in the path of those who wish to invest in new areas of our economy. I, therefore, strongly urge the FCC to resolve DBS questions," the letter said.

Although the letter does not mention Comsat, the District-based satellite company is the first applicant to seek permission formally to provide the service.

The company has pledged to spend more than $600 million to launch the service, which would bring television signals directly form satellites to homes via receiving dishes installed on the premises of the viewer.

Comsat has proposed offering three networks of new programming. Much of the programming would be new shows put together by a Comsat subsidiary, Satellite Television Corp., a venture with a distribution potential to challenge the nation's television networks.