A. Hyatt, Mayor, 78, the curatoremeritus of the department of prints and photographs at the Metropolitan Museum of Art and a man who tempered learning with wit, died Thursday at his home in New York City. He had pneumonia.

Mr. Mayor was hired in 1932 by Willia Mills Ivins Jr., the Metropolitian's first curator of prints. He suceeded Ivins as curator in 1946 and remained in that position until his retirement in 1966. Items that Mr. Mayor added to the museum's engravings and woodblocks by such masters as Rembrandt and Durer included wine labels, mail-order catalogues, which are useful as references on topics such as furniture, and one of the world's finest collections of cigarette insert-cards and similar ephemera. He thought the cards, once cheap and easy to come by and now expensive and rare, attractive as well as interesting.

For several years after becoming curator-emeritus, Mr. Mayor assembled the pictures and wrote the texts for the museum's annual Christmas calendars. Some editions sold as many as half a million copies.

In 1971, he published "Prints & People, A Social History of Printed Pictures." John Canaday, a critic of The New York Times, described it as "a book so good that to comment on its virtues amounts to presumption."

The book expressed Mr. Mayor's view that prints are primarily a means of communication because so many copies of each work can be produced. This distinguishes them from other forms of art such as paintings, of which there can be only one original copy.

In "Prints and People," he described the struggle between the Catholic Church, personified by Savonarola, and the Protestant Reformation, championed by Martin Luther, both using printed materials, in these words:

"Battle by the printed word driven home by the printed picture was as portentous as broadcasting is today, being as difficult for censors to jam. And indeed, Savonarola in the white silence of his cell looked and acted like a radio broadcaster -- a voice in a closet persuading millions."

Of pictures showing life at the French courts of the 18th century, he wrote that they depicted "the ruses and obstacles that could complicate love sufficiently to fill life's vacancy."

Although he made his reputation in prints, Mr. Mayor declined to call himself a specialist.

"One can't be in prints," he once said. "Because they leak out into everything, into city planning, into the law, into dynastic history, into all the technologies. . . . And I always thought that my great viture at the Metropolitan Museum was that I had a wide ignorance. That's the most important thing I contributed. And, though I never knew very much, exactly, I knew where to look it up."

However that may be, Mr. Mayor's purpose in all his endeavors was to be entertaining as well as improving. He once hung a show of comic strips that was immensely popular.

"The idealistic purpose, with which one has sympathy, is that of bringing art to as many people as you can," he once said. "Whether they go there to keep up with the Joneses or to get out of the rain doesn't matter. They may be hooked by suddenly seeing something that really talks to them. It doesn't matter why the come in."

Alpheus Hyatt Mayor was born in Gloucester, Mass., on June 28, 1901. His parents were Alfred Goldsborough Mayor, a marine biologist, and Harriett Hyatt Mayor. He grew up in various towns in New England and in Princeton, N.J. He also spent several years in Europe, where his family went while his father was pursuing his work in such remote reaches as the Great Barrier Reef of Australia. He spoke five languages.

After Princeton, where he got a degree in foreign languages, he taught history or art at Vassar for a year and then won a Rhodes Scholarship and spent several years at Oxford. Until he began his career at the Metropolitan, he was a magazine editor and engaged in various theater projects in New York.

His academic training in art history was virtually nonexistent. But he grew up in the household of an aunt, Anna Hyatt Huntington, a sculptor, and always felt comfortable with art. He once said that he was hired by the Metropolitan because his command of Languages would allow him to educate himself.

Mr. Mayor was the president of the Hispanic Society of America and a member of several learned societies in Spain. He also was a member of the Grolier and Century clubs in New York. Survivors include his wife, the former virginia Sluder, of New York City; a son, Alfred Hyatt, also of New York City; a daughter, Martha M. Smith of Washington; a brother, Brantz Mayor of Hanover, N.H.; two sisters, Katherine Townsend of Montclair, N.J., and Barbara Money of Berkeley, Calif., and two grandchildren.