The comptroller of the currency yesterday cleared the last obstacle out of the path of millionaire Joe L. Allbritton's attempt to gain control of the Riggs National Bank.

Earlier this week the most serious challenge to Allbritton's acquisition of a controlling interest in the bank was removed when Riggs' directors agreed to set aside their opposition to his takeover. The directors agreed to allow Allbritton's tender offer to buy 40.1 percent of the bank's stock for an estimated $70 million to proceed.

The tender offer, however, was contingent on the comptroller's assurances that he would not object to the takeover. That came yesterday.

Stating that the office of the comptroller had reviewed the entire Riggs transaction, the comptroller said the regulatory agency "will not raise any objection" to Allbritton's takeover. The letter added, however, that the review of the transaction should not be construed as an opinion that further review was required.

Whether or not the review was needed was an issue in the legal fight over the takeover, with Allbritton's lawyers saying no and Riggs' attorneys insisting that it was.

The firm that is acting as Allbritton's spokesman said that his purchase of up to 750,000 shares of the stock of the area's largest financial institution is expected to take place as soon as possible after the tender offer ends at 9 a.m. March 30. Allbritton announced yesterday that as of 3:30 p.m., 758,081 shares had been tendered.