Andre Meyer, 81, a former senior partner of Lazard Freres & Co., a respected New York investment banking house, died Sunday at the Nestle Hospital in Lausanne, Switzerland. He had pneumonia and complications from other ailments.

Mr. Meyer was associated with firms bearing the Lazard name for more than 50 years. In 1925, he became a partner of Lazard Freres & Cie. in Paris, where he was born. In 1940, he fled the Nazis and joined Lazard Freres & Co. in New York. He was named senior partner in 1944 and held that position until 1978, when he retired and became a limited partner.

Under Mr. Meyer's direction, Lazard Freres became the investment bankers for some of America's leading corporations, including the Chase Manhattan Bank, the Radio Corporation of America, the Corning Glass Co. and the International Telephone and Telegraph Co. In 1971, Lazard Freres was the principal underwriter for a $33 million public stock offering by The Washington Post Co.

Mr. Meyer was noted in financial circles as an authority on international finance. He served on advisory commissions under Presidents John F. Kennedy and Lyndon B. Johnson. He was a catalyst in the formation of development banks in the Third World.

He was a philanthropist who once made a gift of $2.5 million to New York University and who donated a physics laboratory to Mount Sinai Hospital in New York City and a physiology laboratory to the Memorial Hospital for Cancer in New York. He was an art collector whose pictures -- mainly the work of French impressionists and post-impressionists -- were exhibited at the National Gallery of Art in Washington in 1962.

He also was an intensely private man who once told an interviewer that he was "terribly allergic to any kind of article written about me." By way of explanation, he said that this resulted, perhaps, from "an excess of humility."

Felix Rohatyn, a partner of Lazard Freres and the former head of "Big MAC," the Municipal Acceptance Corp. that was formed to restructure the debts of New York City, said yesterday that Mr. Meyer "had a range for excellence. He worked harder than other people and he enjoyed it tremendously."

Other associates said Mr. Meyer was almost addicted to the telephone, that he arrived in his office at 8 a.m. and stayed until 6 p.m., that he insisted on absolute secrecy in business dealings, the better to control his activities, and that he was quick to anger and quick to forgive. The news of his $2.5 million gift to NYU was made public only at the insistence of the university.

Mr. Meyer, who left much of his art collection to the Metropolitan Museum of Art, felt that philanthropy held a special place in the United States.

"I beleive that people are very generous altogether," he once said in his careful, self-taught English, "and that marvelous results have been obtained here like in no other part of the world. It's a great credit to the American people."

Among well-known persons to whom Mr. Meyer was an adviser were Aristotle Onassis and Mrs. Jacqueline Kennedy Onassis, for whom he occasionally acted as an effort.

The firm Mr. Meyer headed is a partnership. The partners' own money is involved in the investments that they make. The company was started by the Lazard family in New Orleans in 1843. Later, an office was opened in San Francisco and it became the agent for the French government in the purchase of gold found during the California gold rush. The New York office was opened later in the last century. Today, there is a Lazard Brothers Co. Ltd., of London, as well as the Lazard operations in New York and Paris.

Mr. Meyer's business dealings included the buying and selling of the Avis rent-a-car company. According to an associate, a client asked Mr. Meyer to look into the possibility of purchasing the company.Mr. Meyer did so and reported that Avis had lost money in 12 of the previous 13 years and that the profit in the 13th year had been due to a change in accounting methods. The client said he was not interested.

However, Mr. Meyer used Lazard funds to buy Avis for $7 million. Some years later, it was sold to ITT for $44 million worth of ITT stock.

Lazard Freres & Co. did not operate that way when Mr. Meyer joined it in 1940. The company was known for "taking a postion" on deals made by other investment bankers. It did not start many transactions on its own. It never lost money.

Mr. Meyer changed that. He became a member of the boards of RCA and the Chase Manhattan Bank, and Lazard Freres became the primary investment banker for those corporations. Similar arrangements were made with Corning Glass, ITT and other companies.

In 1944, Mr. Meyer was named senior partner by Pierre David-Weil, his predecessor in that post. (The Weil and Lazard families were related and the Weil branch became dominant in the firm.)

Andre Benoit Mathieu Meyer was born in Paris on Sept. 3, 1898. He was educated at the Lycee Charlemagne and the College Rollins in Paris, from which he graduated in 1918. He worked in the investment banking house of Bauer Freres until joining Lazard in 1925.

In the 1920s and 1930s, he helped arrange the merger of the Citroen automobile company and the Michelin tire company. He also acted as an adviser to Owen D. Young, the American author of the Young Plan of 1928. This eased the terms under which Germany was to pay reparations levied against it by the Allies at the end of World War I. Mr. Meyer also took a leading role in supporting the French franc and the British pound in the financial and political crises of the 1930s.

With the rise of Hitler in Germany, Mr. Meyer became an opponent of Nazism. As a Jew, he quietly financed numerous German Jews who fled the persecutions visited upon them by the Third Reich. Although these activities were discreet, Mr. Meyer's name appeared on a Gestapo list of Frenchmen who were to be imprisoned or short after the fall of France in 1940. He narrowly escaped the German invaders and made his way to the United States.

Mr. Meyer had already become an art collector before the outbreak of World War II. His pictures were confiscated by the Nazis and he recovered only two of them when the war was over,

Among Mr. Meyer's honors was membership in the French Legion of Honor, in which he held the rank of grand officer.

In recent years, he had maintained a home at Crans-sur-Sierre, Valais, Switzerland, and an apartment in Paris. In New York, he lived at the Carlisle Hotel.

Survivors include his wife, the former Bella Lehman, whom he married on Dec. 23, 1922, two children, Philippe and Francine, both of Paris, four grandchildren, and five great-grandchildren.