Richard Tinkham, an Indianapolis attorney and former president of the American Basketball Association, is representing a group seeking to buy the San Francisco Giants and move them to Washington.

Tinkham, once a minority stockholder in the Indiana Pacers of the American Basketbball Association, confirmed last night his group has been negotiating with the D.C. Armory Board to rent RFK Stadium.

The group has three weeks left on an option to purchase 50 per cent of the Giants stock from co-owner Bud Herseth, who is asking $5.5 million.

If sucessful in making a deal with Herseth, the group, comprised mostly of New Yorkers, would seek to buy the remaining stock from co-owner Bob Lurie and move the Giants here.

But the Giants are tied to a long lease at San Francisco's Candlestick Park, although Tinkham indicated the lease would not be a major obstacle.

A long lease (through 1987) resulted in the issuing of a temporary restraining order last week blocking the move of the Oakland A's to Denver. The order was issued after the Oakland Coliseum, city of Oakland and Alameda County sued A's owner Charles O. Finley and Denver's Marvin Davis, who bought the club from Finley for a reported $12.5 million.

The judge set Dec. 30 for a hearing on whether the order should be made permanent.