Melville Bell Grosvenor, 80, a journalist, energetic outdoorsman and member of a prominent Washington family who brought expansion and innovation to a major American cultural institution, the National Geographic Magazine, died Thursday at his winter home in Miami.

Mr. Grosvenor, a grandson of inventor Alexander Graham Bell and a former president of the National Geographic Society as well as editor of its magazine for 10 years, died of cardiac arrest.

The son of Gilbert H. Grosvenor, also a former president of the Society and editor of its magazine, Mr. Grosvenor was the father of Gilbert M. Grosvenor, the society's current president and another former editor of the Geographic.

While at the helm from 1957 to 1967 of what is described as the world's largest nonprofit educational and scientific organization, Mr. Grosvenor saw the society's membership rolls and the magazine's list of subscribers grow from 2,175,000 to 5.5 million. Current membership is 10.7 million.

In addition, Mr. Grosvenor, himself a man known for curiosity, zest for discovery and a sense of wonder, increased significantly the society's grants for research and exploration.

A man who as a child had met such legendary figures of early 20th century exploration and discovery as Adm. Robert E. Peary and Roald Amundsen, Mr. Grosvenor was known as the motivating force behind such National Geographic Society-connected projects and expeditions as those that planted the first U.S. flag on Mount Everest and uncovered 2-million-year-old fossil bones of man-like creatures in East Africa.

To the Geographic's readers, one of Mr. Grosvenor's principal contributions came in the area of makeup and layout.

It was at his initiative that photographs were introduced to the elegant if staid front cover of the magazine.

At the outset, such tampering with tradition caused tempest and furor.

"I had grown tired of looking at the same cover," Mr. Grosvenor later recalled. "The staff was against the change. My son, Gil, then a very junior member of the staff, opposed it. One day I called them into my office and tossed 10 magazines on the floor and asked them to pick out the latest issue. They had to sort around.

"Then I tossed 10 sample covers with photos on the floor and said, 'OK, pick out the Japanese issue.' Gil immediately picked up the one with the geisha girl on the cover. So I said: 'That's what we're going to do.' "

The July 1959 issue was the first to carry a picture on the cover. It showed an American flag.

Mr. Grosvenor, who was known for expanding the Society's efforts in book publication and for producing the first National Geographic "Atlas of the World," also introduced a variety of technical improvements in color printing.

He also was credited with initiating the gradual elimination of the yellow oak leaf border that had run for years around the magazine's cover. Many readers protested Mr. Grosvenor's initial move as an act of desecration, and it was not until after his tenure as president-editor ended that the time-honored edging finally vanished.

The dedication in 1964 of the Society's gleaming new Edward Durell Stone-designed headquarters building at 17th and M streets NW has been viewed as a symbol of the expansion of the society and its activities during the tenure of Mr. Grosvenor, who joined the Geographic in 1924.

It is noted, however, that Mr. Grosvenor's connection with the Society goes back to his infancy. He was 5 months old in early 1902 when a great-grandmother guided his hand to help lay the cornerstone for the society's original headquarters, Hubbard Hall, named for an ancestor.

Mr. Grosvenor, born here Nov. 26, 1901, was the first grandchild of Alexander Graham Bell, and the inventor of the telephone tutored the boy, helping to foster his interests in sailing and in the sciences.

Instruction by his father in writing and photography, which began in Mr. Grosvenor's childhood, went on to a degree during his four years at the Naval Academy at Annapolis. It intensified and was expanded to include editing and recognition and development of story ideas when, after a year of sea duty, Mr. Grosvenor joined the Geographic.

A sailing enthusiast for years, he kept his hand on the tiller of his 46-foot yawl, White Mist, after stepping down as editor and president to accept the new post of editor-in-chief, and became chairman of the trustees. He later became chairman emeritus and in 1977, editor emeritus.

"The whole thing is to keep going," he observed in an interview at 72. "Keep on doing things. If you sit on your fanny, you're gone. You may go broke, but you'll have fun."

Mr. Grosvenor's marriage to Helen North Rowland ended in divorce. In addition to Gilbert, they had two other children, Helen Lemmerman of Magnolia, Mass., and the late Navy Capt. Alexander G. B. Grosvenor.

Mr. Grosvenor married Anne E. Revis in 1950 and they had a son, Edwin of New York, and a daughter Sara, who is attending the University of Missouri Journalism School. Survivors also include four sisters, Gertrude Gayley of Coconut Grove, Fla.; Dr. Mabel H. Grosvenor of Washington; Lilian Jones of Aldie, Va., and Carolyn Myers of Washington, and seven grandchildren and four great-grandchildren.

Mr. Grosvenor maintained a home in Bethesda and had a summer home in Nova Scotia.