The D.C. City Council voted 9 to 3 last night to override Mayor Marion Barry's veto of regional interstate banking legislation and set for itself a 30-day deadline to address the issue of allowing the nation's largest banks to enter the District.

The council vote climaxed an intense, month-long lobbying effort that pitted the local banking community, which favors a limited form of interstate banking, against Citicorp of New York, the nation's largest bank holding company and an aggressive contender for a District banking license.

It was also the third consecutive time in 11 months that the council has overridden mayoral vetoes.

While the local banking community won a clear-cut victory, a Barry administration aide expressed disappointment in the vote but claimed the mayor had successfully forced local banks to consider investments in the city's distressed areas.

Courtland Cox, an assistant to the deputy mayor for economic development, said "it is not over for money-center banks," referring to the nation's largest banks.

Lucius P. Gregg, chief spokesman for Citicorp, said after the vote that he did not want to talk with reporters.

The regional banking legislation now must undergo a 30-day congressional review period before it becomes law. However, the council's action paves the way for banks in the District and 11 southeastern states to merge with or acquire each other.

Two acquisitions have been announced. Sovran Financial Corp. of Norfolk plans to acquire D.C. National Bankcorp, parent company of D.C. National Bank, and United Virginia Bankshares' plans to buy NS&T Bankshares Inc., the holding company for NS&T Bank.

The battle for council members' votes reached unprecedented levels after Barry, who originally introduced the banking legislation, proposed amendments to allow the nation's largest banks to enter the District within two years -- or earlier if large investments were made in distressed areas of the city -- and then vetoed the banking bill after the council did not approve the amendments.

Citicorp pledged to provide $100 million in loans for small businesses and neighborhood development projects and, some council members said last night, local banks increased their investment commitments after the mayor's veto.

Last night, for two hours in a steamy council chamber, City Council members took turns expressing their views on the banking issue before a capacity audience made up largely of representatives from the local banking community.

City Council member Wilhelmina J. Rolark (D), whose Southeast Ward 8 has some of the most distressed areas in the city, said lobbying by Citicorp and the local bankers made her feel like a "debutante being wooed."

She said Daniel J. Callahan III, chairman of American Security Bank, toured her ward and pledged to invest about $28 million there. Callahan also toured Democrat H.R. Crawford's Ward 7, and Crawford last night listed $27.5 million worth of projects that Callahan had agreed to finance in his ward.

City Council member John Ray (D-At Large), who with Frank Smith (D-Ward 1) and Nadine P. Winter (D-Ward 6) supported the veto, urged the council not to allow Citicorp's loans in South Africa to influence their decisions despite the fact that the local bankers had made that involvement an issue. Ray noted that some banks in the District's 11-state interstate region also do business with South Africa.

But John Wilson (D-Ward 2) said that he had toured two New York City boroughs, the Bronx and Queens, and concluded that "if Citicorp has all this money, they have plenty of depressed areas to invest it in."

Although Council Chairman Daivd A. Clarke characterized the council's action as "a step in the right direction," he said the council has "not turned down the issue of the national approach."

City Council member Charlene Drew Jarvis (D-Ward 4) promised that within a month her Committee on Housing and Economic Development will send the full council a new bill to resolve the question of national banking by addressing the issues that were the basis for the veto. Barry also wanted the executive branch rather than the council to review applications for bank acquisitions.

Local banks had argued that proposals to allow Citicorp and other large banks to enter the District market in two years or less would create unfair competition. Michael Ryan, chairman of the D.C. Bankers Association, said he was "pleased" by the council's action.

Barry has already introduced a bill incorporating a "trigger" provision that would allow any bank outside the 11-state region to enter the District market in two years and granting special entry to any bank that would invest $100 million in the city's distressed areas and create 200 new jobs. Jarvis said her committee will seek a compromise on those issues and will consider such questions as when Citicorp and the other large banks should be allowed to open branches in the District and whether they should be allowed to acquire District banks.

Citicorp has provided financing for commerical loans in the District since 1979, but by law it is prohibited from collecting deposits here without a banking license.

In other action, the City Council gave final approval to a mandatory seat belt law, which would require anyone riding in the front seat of a motor vehicle driven in the District to wear a seat belt. A driver or passenger could each receive a $15 ticket for not wearing a seat belt, but a police officer could issue such tickets only after stopping a driver for some other offense.