Attorney Guy Martin, 69, who has been associated with International Bank longer than any other individual, yesterday was named the new president of the holding company, effective Jan. 1, 1981.

Martin immediately will assume his additional duties as vice chairman of the board of directors, vice chairman of theexecutive committee and deputy chief executive officer.

In his role as a director of the company since 1952 and as legal counsel, Martin is familiar with all its operations and owns 1.2 percent of IB's stock, a spokesman said yesterday. He is senior partner in the firm of Martin, Whitfield, Smith & Bebchick.

The primary stockholder is Gen. George Olmsted with 36 percent. Olmsted, 79, who said earlier this year he has no plans for retirement, will continue as chairman and chief executive officer.

International Bank also announced the appointment of Jerauld L. Olmsted, the general's son and senior vice president, to the executive committee, and Henry N. Conway Jr., senior vice president for international banking and finance, to the board of directors and executive committee.

Like Olmsted, Martin is a veteran of World War II. He served in the U.S. Navy as a combat intelligence officer and later with the Office of Strategic Services in Asia. After the war he served as general counsel to the American Claims Commission. He is a graduate of Oxford University and Yale Law School.

International Bank, a holding company for diversified financial services and merchant banking operations, has investments in manufacturing, insurance, finance, leasing, foreign corporate formation and maritime administration and overseas banking.

During the first half of this year its profits totaled $7.7 million, down from $8 million in the first half of 1979. In August, IB made a public offering of $20 million in subordinated debentures.