Joe L. Allbritton, chairman of the board of Riggs National Corporation, is attempting to form a group of Washington-area investors to try for a major league baseball expansion team, it was learned.

Allbritton sent a letter yesterday to potential investors inviting them to a luncheon Tuesday at a downtown Washington hotel. Allbritton reportedly would like to put together a group of about 20 people, each of whom, including himself, would invest $2 million. He is not interested in acquiring an existing team, sources said.

Allbritton's attempt to put together the group means that the Washington area now has four individuals or groups trying for a big-league baseball team here. The others are Jack Kent Cooke, owner of the Washington Redskins; real estate developer Ted Lerner and Robert Schattner, former dentist and the developer of Chloraseptic and other products, and builders Oliver T. Carr and James Clark.

Former baseball commissioner Bowie Kuhn, who has been linked with the Carr-Clark group as a possible executive, also might be sought in some capacity by Allbritton, it was learned.

The D.C. Baseball Commission, comprising area business leaders and political officials, is in the midst of a drive to sell 10,000 season tickets by July 31 to show Commissioner Peter Ueberroth and other baseball executives that the area has solid fan support. A commission spokesman said that as of yesterday, $3,614,625 -- worth 6,375 season tickets -- has been deposited in area banks.

Although Allbritton was not available for comment, his spokesman, George Beveridge, confirmed that the former owner of The Washington Star was interested in baseball for Washington and had sent the letter.

"Mr. Allbritton has taken this action as a private citizen, not as a banker," Beveridge said. "It's totally exploratory. He wants to see the extent of the interest in the business community."

In the letter, Allbritton noted that Ueberroth's cancellation of baseball's scheduled summer meetings next month because of the threat of a players strike has "some disappointing aspects in regard to Washington's drive" to get a club. But he also pointed out the delay could have some positive aspects.

"The splendid efforts launched by the D.C. Commission on Baseball already have mobilized a great deal of tangible evidence of Washington's widespread community support," Allbritton wrote.

"It has been my feeling for some time, however, that business and professional leaders of our community might be in a unique position to do even more on behalf of returning baseball to the Nation's Capital. There is at least an obligation to try."

Ueberroth said in March that cities trying to acquire a major league expansion team should try to fulfill three criteria: fan support, political support and multiple ownership with local roots.

The D.C. Baseball Commission's target date for an expansion team is 1987. There are about 10 cities hoping to get a team, with Denver and Washington considered the leading contenders.

Allbritton, a 60-year-old native Texan who lives in Washington, owns WJLA-TV-7 and other broadcast properties. He won a bruising takeover battle for Riggs in 1981. After paying $70 million for about 40 percent of Riggs' stock, Allbritton formed Riggs National Corp., a holding company that owns only the bank.

He also owns Allbritton Communications, which, besides WJLA, includes the Trenton Times and several other newspapers.