Marcel Breuer, 79, a monumental figure among modern architects and designers, died Wednesday at his home in New York City. He had a heart ailment.

Mr. Breuer was esteemed not only as an architect and loved as a teacher, but regarded as the father of modern furniture design.

As an architect, he was responsible for some of the most important buildings across the United States. As a teacher, his influence has been even more widespread. Some 200 of the country's most important architects were among his students.

But all of his major innovations in furniture design came to him before he was in his mid-30s.

By his own account, his major breakthrough in furniture design, the use of tubular steel, came to him one day while riding his first bicycle. He noticed how the tubular steel was bent to make the handlebars.

From this observation came his famous 1925 "Wassily" chromed tubular steel and stretched leather sling chair and the 1927 "Cesca" cantilevered steel-and-cane chair. The "Cesca" chair in reproductions has become the most familiar chair of the 20th century, as common in breakfast rooms as the Thonet chair was in 19th century cafes. Mr. Breuer's tubular steel furniture obviously also was influenced by the Thonet bentwood chairs, which were made in Vienna, Austria, where he briefly studied.

Museum of Modern Art design curator Stewart Johnson and historian Chistopher Wilk have been working with Mr. Breuer for three years on an exhibition of his furniture to open at the museum on July 25.

"He had rather talk about his latest building than his furniture of 56 odd years ago," said Wilk.

Although Mr. Breuer might not have agreed, Johnson said he believes Mr. Breuer will be better remembered for his furniture designs than for his architecture.

"The two were not of the same order of importance," Johnson said. "Architects had designed modern buildings before Breuer -- his architecture was in the main stream. But Breuer designed the very first modern furniture. Before him, there was no truly modern interior design. Early 20th century architects had to make do with Thonet bentwood.

"His idea of tubular steel became known among other desingers instantly, and the concept spread like wildfire. Before long, everybody -- Mies van der Rohe, Mart Stam and Le Corbusier -- were all doing steel furniture.

"The cool austerity, the sleek gleam of metal, was exactly what had been needed to bring the modernist interiors to life. Had he accomplished nothing beyond that first tubular steel chair, his signal importance would remain for his vision of . . . the machine for sitting in, the chair with the handlebars."

Mr. Breuer later designed cutout plywood and laminated wood furniture, some of which may be mass produced.

Peter Blake, head of the Catholic University architecture department and a friend of Mr. Breuer, wrote a book of interviews with him. Blake once wrote that somebody, sooner or later, would have invented furniture of continuous tubes of chromium-plated steel, and "translated the American traditions of wood and stone building into an entire modern idiom, or made modular, precast concrete into a building unit as flexible as brick. But the fact is that Breuer was really the first one to do it, and that his prototypes have been often copied but rarely improved upon over the decades."

Mr. Breuer was born on May 21, 1902, in Pecs, Hungary. After studying there in Vienna, he went to the Bauhaus design school in Weimar, Germany. The school, which the was under the direction of Walter Gropius, is credited with developing the international style in architecture, which has dominated building for the past half-century. After studying construction from 1920 to 1924, Mr. Breuer became the master of the Bauhaus carpentry shop. He was only 23 when he got his great idea about tubular furniture.

Mr. Breuer was the last of the great Bauhaus architects who immigrated to the United States during the Nazi era in Germany. He came to the United States in 1937 at the invitation of Gropius, by then a professor at the Harvard University Graduate School of Design.

Mr. Breuer also joined the Harvard faculty. In the nine years that he was an assocaite professor there, he taught students who have become among the most important architects of the mid-20th century.

His most successful student was Philip Johnson. Johnson's writings about what he called the International Style introduced Mr. Breuer, Mies van der Rohe and Gropius to America. When Johnson, already well known as an architecture critic, curator and historian, decided in his mid-30s to become an architect, he chose Mr. Breuer and Harvard as his teacher and school.

Like Mr. Breuer, Johnson and another Breuer student, I. M. Pei, won gold meadals, the American Institute of Architects highest commendation. (Among other honors, Mr. Breuer later won the French architecture gold medal.) The Harvard professor also taught Edward Larrabee Barnes, Ulrich Franzen and Paul Rudolph, all of them among the best known of today's architects.

Peter Blake said last night that Mr. Breuer's "English was always terrible, but he communicated through his personality, his warmth and his talent. He was the great architecture teacher. He produced an enormous variety of architects through his warmth and clarity, who then went off in their own directions.

"Everybody was always crazy about him. He was a terrible chess player, but all of us always let him beat us because he enjoyed winning so much. It's funny, he was not an intellectual sort of person, he was really sort of a peasant, but his work was sophisticated. I think he is already being rediscovered."

In 1946, Mr. Breuer left Harvard to set up his own architecture office in New York City. "He didn't have any work," said his associate, Herbert Beckhard, "so I worked free for him for six months, until he got a commission. It was certainly cheaper for me than graduate school and a great deal more rewarding."

Mr. Breuer's other associates, who still practice under the name of Marcel Breuer Associates, are Robert F. Gatje, Hamilton P. Smith and Tician Papachristou.

"He didn't insist that we always do things his way," said Beckhard. "He didn't stifle you, he opened avenues. Even after he retired in 1976, I would take work to his house or apartment. He wouldn't say much, but he would make a point or two. I remember him best in his lumberjack shirt and chino pants as we worked in his country house in Wellfleet, Mass."

Among Mr. Breuer's most noted buildings are the UNESCO headquarters in Paris, the Whitney Museum of American Art in New York, buildings at Vassar College in Poughkeepsie, N.Y., and the University of Massachusetts in Amherst, and St. John's Abbey Church in Collegeville, Minn.

In Washington, he designed the Department of Housing and Urban Development, the Hubert Humphrey Building of the Department of Health and Human Services, both within view of the Capitol, and the American Press Institute in Reston. His design for a Franklin Delano Roosevelt memorial was turned down.

In later years, most of his buildings were big commercial structures. But like most architects, he designed houses earlier in his American career. His houses were greatly influenced by American regional architecture. He liked the juxtaposition of wood, stone, glass and steel. He planned what he called bi-nuclear houses, which gave children and adults separate spaces. His 1949 split-level "butterfly" house built in the Museum of Modern Art garden was influential.

At a symposium at the Museum of Modern Art in February 1948, Mr. Breuer made the point that you couldn't count on redwood, imperfections and imprecision to make architecture human. And he said you couldn't make a building human by "camouflaging architecture with planting, with nature, with romantic subsidies."

"On the other hand, he said, if the International Style meant only mechanistic and impersonal, rigid forms, then down with it. He called the name an unhappy one -- just an unhappy as "fuctionalism." While in Washington to dedicate the Humphrey building he said, "I never called my architecture International Style. I have never wanted to be a trend."

What he did like was contrasting elements of nature and man used at the same time, as he said, to bring happiness -- "the crystallic quality of an unbroken, white flat slab . . . in contrast to the rough, 'texture-y' quality of natural wood or broken stone . . . the sensation of man-made space, geometry and architecture . . . in contrast to organic forms of nature and man. 'Sol y sombra,' as the Spanish say: sun and shadow, not sun or shadow."

Since his illness, Mr. Breuer had designed tapestries that were made in France and used in some of his buildings, including the Humphrey building and the API here. Earlier, he also designed monumental pieces of architectural sculpture.

Mr. Breuer's marriage to the former Martha Erps ended in divorce.

His survivors include his wife, Constance Crocker Leighton, whom he married in 1940, of New York City and Wellfleet, a son, Tomas Breuer, also of New York, and a daughter, Francesca Burnes of Flaine, France.