Mochtar Riady, the wealthy Indonesian banker who is attempting to buy Bert Lance's stock in the National Bank of Georgia, is an experienced ectrepreneur with varied business interests in Southeast Asia, extending from Jakarta to Singapore and Hong Kong.

Sources in New York and Jakarta indicate that Riady, about 45, has a private fortune in excess of $10 million and enjoys "an excellent reputation" in business and banking circles.

He is an ethnic Chinese whose family has been in Indonesia for four generations he told Robert B. Anderson, the former secretary of treasury who describes his role as "something between advising and representing Riady.

Riady made his offer for the Lance shares to Thomas Mitchell trustee for Lance, who committed himself to sell the stock by Dec. 31. The Riady offer is conditioned on gaining a controlling interest in the bank and on his being "acceptable" to and "welcomed by," the community. It was not clear whether Riady is attempting to buy 51 per cent of the bank stock.Lance's holdings of NBG stock amount to 16 per cent.

Mitchell could not be reached yesterday for comment on Riady's offer, but Anderson said he thought the matter would be settled one way or the other "in several days."

Riady is the chief executive officer of the Bank of Central Asia, the third-largest private banking firm in Indonesia with about $100 million in assets. The bank's profits last year are estimated by a New York source at $500,000.

Riady's personal fortune has been built on a host of business enterprises in addition to his bank. He is the founder and a director of the Multinational Finance Corp. of Jakarta, an envestment consortium that has put him in close touch with key banks in the United States and Europe.

Partners with Riady's bank in the consortium include the Chemical Bank of New York, the Royal Bank or Scotland, Jardine Fleming of Great Britain and the Long-Term Credit Bank of Japan, in Tokyo.

A spokesman for the Chemical Bank, who described the Multinational Finance Corp. as "not big, but certainly a multimillion-dollar operation," said that Chemical has a 23.75 per cent interest, and that Riady's bank has 27.5 per cent. "We regard Mr. Riady as an astute and reputable banker," the Chemical spokesman said. He added that Chemical first began dealing with Riady about four years ago.

Riady's other diverse business interests include the Pancatex Spring Mills Ltd., of which he is chairman of the board, and Serba Motors Ltd., of which he is a director, both in Indoneasia. He is also chairman of the board of Lippo Trading Ltd. in Singapore and a director of two companies in Hong Kong, the P.T. Bhirawa Steel Co. and the Lippo Finance Co., Ltd.

Riady reportedly also has an interest in flour milling and construction companies, and is prominent in the Indonesian Bankers Association.

New York bankers remain puzzled by Riady's interest in the National Bank of Georgia. Anderson, who is a private consultant on international investment operations with offices in New York, said he met Riady several years ago in Jakarta. When Riady expressed interest some months ago in buying a banking property in the United States, Anderson said, he mentioned the National Bank of Georgia as a prospective purchase.

Speculation included a guess by a New York banker who claims to know Indonesia well that Riady might be fronting for government officials in Indonesia anxious for a way to do a good turn for the Carter administration. "They think of this country like a 'regime' similar to their own, and they just don't realize that such a ploy wouldn't work," he said.

Others think that Riady may be just as described by Anderson, an aggressive businessman ready to make a major investment in this country to round out his holdings, and who views the Natonal Bank of Georgia as one where the seller urgently needs to find a buyer.

Riady has been in the United States within the past 10 days, but returned to Jakarta at the beginning of this week.