The New York State Banking Board reversed yesterday a ruling made four months ago and approved the application of a Middle East investor group to acquire Financial General Bankshares Inc., a $2.6 billion multibank holding company based in the District.

The banking board's 9-2 vote clears the last regulatory obstacle in a four-year fight by the Middle Easterners to gain control of Financial General.

Approval of the investors' application to form a holding company to acquire Financial General already has been approved by the Federal Reserve Board.

However, authorities in some states where Financial General operates its 12 affiliate banks had objected to the takeover. While New York banking officials maintained their opposition, authorities in other states, including Maryland, withdrew their objections.

Financial General holds controlling interest in Bank of Commerce in New York City and Community State Bank in Albany.

The New York banking board rejected the Middle Easterners' application in November, amid strong protest from groups that opposed the idea of Arab investment in U.S. banks.

However, an amended application filed by the investors in January apparently proved satisfactory to the banking board during a lengthy meeting yesterday. The key in that amended application is an agreement between the Middle East group and four directors of Bank of Commerce.

Under that agreement, the directors, acting as individuals, will form an investment group to purchase Financial General's 67 percent interest in Bank of Commerce. The buyers have until March 1983 to exercise their agreement with Financial General.

Based on Bank of Commerce's current book value, the transaction would amount to an estimated $31 million.

The agreement further calls for the banking board to approve the Middle Easterners' plan to buy the Albany bank and establish a branch in the more lucrative Manhattan market.

The next step in what has become one of the longest takeover battles on record is to make a tender offer for Financial General's stock, according to Robert A. Altman, a Washington lawyer whose firm represents the Middle East group.