Former Washington Star publisher Joe L. Allbritton yesterday completed his previously announced plan to purchase more than $29 million in Riggs National Bank shares, making him the largest stockholder in the Washington area's biggest financial institution.

About 10,000 fewer shares actually changed hands than were originally contemplated, however.

The transaction, completed about 1 p.m. yesterday, came after a brief but unexplained delay that was revealed last weekend.

Informed sources said yesterday that the postponement was necessary because of a last-minute decision not to sell a small portion of the shares being offered and a routine Securities and Exchange Commission review of the acquisition -- normally conducted whenever a major block of shares in a publicly traded firm is to change hands -- that had not been completed.

After receiving a letter from the comptroller of the currency, saying that the bank regulatory agency would not object, Allbritton purchased -- at the agreed-up price of $67.50 apiece -- the 386,645 shares previously owned or controlled by Dynalectron Corp. Chairman Jorge Carnicero.

The former Star owner originally had agreed to buy 397,545 shares owned by the Carnicero interests, but one unidentified seller in the Carnicero group decided to retain about 10,000 shares.

Allbritton now owns more than 15 percent of the 2.99 million Riggs common shares outstanding. To date, he has not indicated whether he plans to take an active role in the bank's management, but sources have said he is interested in Riggs primarily as an investment. He could not be contacted for comment on the transaction yesterday.

Riggs Chairman Vincent Burke Jr. yesterday welcomed Allbritton "into our official family" but declined to say whether the former Texas banker would join the bank firm's board.

He said such information will be included in a proxy statement for the bank's annual meeting, which has been delayed this year until April 22 to prepare material on a proposed bank holding company, to be called Riggs National Corp., that stockholders must approve. The proxy statement should be sent out about a month before the April meeting, Burke added.

Carnicero said in an interview that both he and his daughter, Jacqueline Carnicero Duchange, would remain on the 25-member board. If another Carnicero nominee to the board, Dynalectron officer Merlon Richards, steps down, that would open a seat on the board for Allbritton.

Dynalectron is a McLean-based technical services, engineering and energy company controlled by Carnicero, who has said he would use proceeds from selling Riggs stock to boost his investment in Dynalectron.

Allbritton, a former director of American Security Corp., heads the Washington-based Allbritton Communications Co., which owns television stations that formerly were the property of The Star (including WJLA-TV here) in addition to newspapers in New Jersey and Massachusetts. Allbritton sold the Washington newspaper to Time Inc.

Riggs' assets on Dec. 31 were a record $3.15 billion compared with $2.69 billion a year ago. The bank also owns Central Charge Service, the region's largest credit-card business.