The Federal Communications Commission has decided to appeal to the Supreme Court a lower court ruling last month which threw out the agency's existing regulations on common ownership of a newspaper and broadcast station in the same area, sources said yesterday.

The ruling, by the United States Court of Appeals here, ordered the FCC to draw up regulations under which companies owning a newspaper and a broadcast station in the same town would have to divest itself of one of them unless the joint ownership was "clearly in the public interest."

In January 1975; the FCC adopted a rule that prohibited newspapers in the future from acquiring radio or television stations in the same market, but allowed almost all existing joint ownerships to continue under a "grandfather clause."

The appeals court decision last month, written by Circuit Chief Judge David L. Bazelon, said the FCC should have applied the ban retroactively except in those cases where the evidence clearly disclosed that the cross-ownership was in the public interest. It ordered the commission to adopt new rules under which the divestitures would take place.

On Tuesday, at the FCC's request, the appeals court agreed to stay its order to the commission on the condition that FCC file its appeal with the Supreme Court by April 22. The commission has said it would comply.