The Department of Commerce yesterday urged the Federal Communications Commission to promptly authorize Communications Satellite Corp. to begin satellite television service.

Reiterating a position recently taken by Commerce Secretary Malcolm Baldrige, the department's National Telecommunications and Information Administration said in a letter to the FCC that the new Comsat service must be in operation during the early part of the current decade so it can compete with other television technology.

Comsat has asked the FCC to authorize the start-up of $600 million program that would offer three networks direct broadcast satellite service (DBS). It would be the first service formally bringing satellite television signals directly to homes.

Broadcasters and representatives of business radio firms are fighting the proposal, claiming that the authorization would hamper U.S. policy in allocating spectrum space, and potentially could threaten the conventional over-the-air television market.

Next week, the FCC will begin formal hearings on the matter, although Congress has not confirmed Mark Fowler, the Reagan administration's choice to head the commission. Fowler has yet to address the policy questions raised by the Comsat application.

But the Reagan administration, citing its desire to advocate a free-market approach to regulating such new broadcast services, said the Comsat service would stimulate investment and job creation, while further developing related businesses such as the satellite and earth-station construction fields. r

"DBS is an expensive, high-risk venture," the Commerce Department said in its filing. "Comsat's initial investment alone will exceed $600 million, with costs and competition increasing rapidly. For DBS to compete effectively, it must be operational by the early 1980s, so prompt action by the FCC is needed."

Further, the department said that other nations already are starting to introduce similiar services, and speedy regulatory approval of the Comsat proposal is likely to aid the nation's competitive posture in the technology business.