A federal judge yesterday extended a temporary restraining order barring the takeover of Riggs National Bank by millionaire Joe L. Allbritton for another six days. At the same time, Allbritton agreed to extend the tender-offer period during which shareholders may withdraw stock they have offered to sell to him.

U.S. District Court Judge Norma Holloway Johnson indicated she will rule Tuesday on whether to grant a preliminary injunction that Riggs has sought in order to block the takeover of the bank by Allbritton.

Attorneys for the city's largest financial institution yesterday reiterated arguments that Allbritton has failed to disclose adequate information to shareholders upon which to base a decision to buy or sell stock and failed to disclose his ultimate plans for the bank, which they said might result in the bank's assets being used to help finance the bank's acquisition.

Lawyers for Allbritton charged that Riggs management was trying to delay Allbritton's acquisition of 600,000 or more shares of stock long enough to ensure that neither Allbritton nor any other minority shareholder could exert significant control over the bank.

In fact, according to Allbritton's attorneys, Riggs had formulated a plan to foil any change in control, setting in motion a proposal for a bank holding company that would make it more difficult for minority shareholders to elect directors to the bank.

Allbritton's attorneys argued that Riggs management initially warmly welcomed him to the bank, but then issued a statement saying that it is not in the bank interest for any shareholder to own more than 15 percent of the bank's stock.

Riggs lawyers said the policy was not aimed at Allbritton, although it was adopted at the same time he was acquiring 15 percent of Rigg's stock, becoming the largest shareholder.

"A large bank in a large city should not be controlled by the whim of one person," said Riggs lawyer Fred Vinson.

Allbritton's attorneys said yesterday that Riggs directors had voted to offer long-term contracts to the bank's management to protect them or put them in a position to profit from a buy-out if Allbritton takes control of the bank. However, a brief filed by Riggs attorneys noted that both Chairman Vincent Burke and President Daniel Callahan had said they will not accept such contracts.