The biggest stockholder of Financial General Bankshares Inc., Eugene B. Casey, disclosed yesterday he will support efforts of Middle Eastern stockholders to elect three insurgents to the company's board of directors.

In a report to the Securities and Exchange Commission, Casey said he will vote the 10 percent of Financial General's stock he owns in favor of the nominees of Kamal Adham of Saudi Arabia.

Casey disclosed he also plans to vote for a resolution proposed by Adham urging Financial General to drop its opposition to being taken over by Adham and two associates from Kuwait and Abu Dhabi.

Casey said the three Middle Easterners, who already own about 18 percent of Washington's third-largest banking company, "are major shareholders . . . I believe that they are entitled to representation on the board."

Casey owns about 10 percent of the voting stock of Financial General, slightly more than in controlled by Chairman of the Board B. F. Saul II.

Casey sits on Financial General's board, as does his son, Gene Casey Jr. An enormously wealthy landowner and investor, Casey has offices in Gaitherburg and a country home overlooking the Shenandoah River.

The swing of Casey to Adham's camp leaves the major blocks of stock in the $2.2 billion bank just about eveny divided.

Saul and the company's management originally claimed about 37 percent of the voting rights, but that included Casey's shares. Now the management holds about 27 percent, with 28 percent pledged to the other side.

The remaining 45 percent of the stock is in the hands of thousands of investors, big and small, who will decide who gets on the board at Financial General's annual meeting April 29 in Richmond.

A spokesman said last night Financial General is preparing a letter to stockholders commenting on Casey's decision but can't respond at this time because of SEC rules. The SEC must approve in advance any statements made to influence the vote in corporate election.