Joe L. Allbritton, chairman and chief executive of Riggs Bank and owner of television station Channel 7, announced late last week that he had sold two New Jersey newspapers to an affiliate of Media General of Richmond for an undisclosed price, estimated to be $50 million to $60 million.

Garden State Newspapers purchased The News of Patterson and The Dispatch of Union City from Allbritton Communications Co., a media company wholly owned by Allbritton.

The newspapers, which Allbritton bought in 1977, have a combined circulation of 75,000.

Media General owns 40 percent of Garden State Newspapers.

The companies involved would not disclose the terms of the sale.

Bruce Thorp, newspaper analyst for John Morton & Co. of Washington, said that based on circulation and location, Garden State probably paid no more than $60 million for the two Northern New Jersey newspapers, or $800 per subscriber.

A spokesman for Allbritton said the sale leaves Allbritton Communications with three daily newspapers, which have a combined circulation of 85,000, and five television stations.

The newspapers are The Times of Trenton and two smaller dailies, The Standard Observer of Irwin, Pa., and The Westfield Evening News of Westfield, Mass.

In addition to Channel 7, the TV stations are in Lynchburg, Va., Charleston, S.C., Little Rock, Ark., and Tulsa, Okla.

Garden State's acquisitions are the latest in a series of aggressive purchases aimed at expanding the newspaper company's stronghold in small newspaper markets and in helping Media General expand its product line, analysts said.

During 1985, Garden State Newspapers acquired two daily newspapers in Northern New Jersey and the Sparks Newspapers in Alameda County, Calif.

It also bought two dailies and six weeklies in the Boston area, which it sold this year to Harte-Hanks Communications in exchange for seven daily newspapers in Washington, Ohio, Michigan and Texas.

Media General, which earned $39.8 million on revenue of $548 million in 1985, owns newspapers, publishing and cable operations, including the Richmond Times-Dispatch and Media General Cable of Fairfax County.