BERT LANCE'S financial affairs are a lawyer's delight. Their complexity is matched only by their ambiguity. His transgressions never seems to be quite criminal, but it is equally true that there is, in his career, a certain pattern of business that does not sit quite square. The character of his current activities is becoming increasingly public through the litigation over Financial General Bankshares, Inc. That's the bank holding company that Mr. Lance and his associates have been trying to take over with the assistance of Arab investors. Last week the Securities and Exchange Commission charged Mr. Lance and his associates with working together to conceal, in violation of law, the extent of their purchases of FGB stock.

Mr. Lance is industriously, and profitably, exploiting his Carter connection. When lawyers were trying to take testimony from him earlier this month in the takeover cases, Mr. Lance swept out at midday, grandly announcing that he was off to lunch with Mr. Carter at the White House. He wasn't able to come back next day because, as his lawyer explained it to the judge, he was off on a 10-day trip for "a series of meetings with heads of state in Europe in connection with . . . the Friendship Force."

The Friendship Force? It's one of those people-to-people things that Mr. Carter started when he was governor of Georgia. Upon inquiry, the White House murmured, unhappily, that the trip had no official status. Which heads of state did Mr. Lance see - the queen of England and the president of France? His lawyer was not explicit on that point.

Mr. Lance has a vast talent for this kind of amiable hokum and self-promotion. Any American over the age of 9 ought to be able to recognize its quality without much difficulty. But it appears that Mr. Lance is no longer playing to an American audience. Here we come back to Financial General Bankshares, the holding company, with its $2.2 billion in assets and its 15 banks - some of which, incidentally, serve the Washington area. It was FGB that sold Mr. Lance his stock in that Georgia bank several years ago - the stock around which his troubles last summer revolved. By late 1976 FGB itself was up for sale and Mr. Lance briefly considered buying it, until Mr. Carter named him director of the Office of Management and Budget.

As a condition of confirmation, Mr. Lance promised a Senate committee that he would stay entirely away from the banking business while in office. But last April, according to the SEC, he met with the seller and the buyer of FGB. In office or out, Mr. Lance seems never to have been very far from FGB.

Last September, Mr. Lance was finally forced to resign from OMB. In October, he was retained by Agha Hasan Abedi, a Pakistani banker operating out of London, representing Arab clients with oil money to invest. By then FGB's new owners had fallen into a blazing internal dispute. Mr. Lance quickly drew Mr. Abedi and tha oil money into the dissident stockholders' plans to take control of FGB and kick out the incumbent management. According to the management's lawyer, Mr. Abedi meanwhile paid off Mr. Lance's $3.5 million loan from a Chicago bank. By December, Mr. Lance was also dealing with a Saudi investor, Ghaith Pharaon, who wanted to buy Mr. Lance's stock in the Georgia bank.

Mr. LAnce's wealthy new friends from the Middle East may well be under the impression that they are buying, along with the stock, a degree of access to political power in this country. Only one person can demonstrate to them convincingly that they are mistaken, and that is President Carter. Surely he must realize by this time that, given any shred of presidential favor at all, the ingenious Mr. Lance will rapidly find a way to convert it into his favorite asset, dhares of stock in banks.