The staff of the Federal Communications Commission yesterday ruled that Communications Satellite Corp. improperly charged its customers for lobbying expenses and ordered the company to desist and to turn over its books to the commission.

The decision comes in response to a complaint filed by Pan American Satellite Co., which charged that Comsat was passing along the cost of its lobbying efforts against a Reagan administration proposal to allow private international satellite systems.

Comsat did not respond to yesterday's FCC announcement. Comsat can appeal the staff ruling to the full commission. The ruling will be issued formally next week.

Comsat, a major member of the Intelsat, has stated publicly that private competition would undermine the global satellite communications consortium that carries most of the world's international telecommunications traffic.

Responding to the PanAmSat complaint, Comsat, a quasi-governmental organization, denied to the commission that it was engaged in lobbying activities.

An FCC staff attorney said that, since the amount spent on lobbying was not known, Comsat would be required to submit its records to the commission so that a rate correction could be made. Comsat will be required to submit regular quarterly information on its lobbying activities to assure that the costs are not improperly allocated.

The Commission also said that Comsat should not be able to pass along to its customers the portion of its fees to Intelsat that go into political lobbying. Intelsat has retained several major lobbying organizations -- including Gray & Co. -- to fight the private satellite proposals.

Historically, the FCC has required regulated companies such as American Telephone & Telegraph Co. to pass along lobbying costs to shareholders rather than customers.