Anthony F. (Tony) Janson was in from the beginning on what has become, in fact, a family book: the encyclopedic "History of Art," which his father, the eminent H.W. Janson, first gave the American art world in 1962.

Hopes were high from the beginning.

"I had just gotten out of college, and was helping read proofs" at the publishers, recalled Tony Janson recently during an interview at the National Gallery of Art.

"An editor I was working with at Abrams said he thought 'History of Art' might turn out to be more than just another art book. The break-even level then for an art book was about 3,000 copies, and that was what they were shooting for on most of their printings. But this man said he would not be surprised if Pop's book didn't do a great deal better -- maybe as much as 60,000 copies. Twenty times the normal expectation! I was amazed."

Now, 24 years later, the verdict is, you might say, in. It's not just that "History of Art" is history's bestselling art book. Its first two editions have sold a mind-boggling 3 million copies. That's almost exactly twice as many copies as that current nonfiction phenomenon of the industry, "Iacocca: An Autobiography," sold during its first year on the market (1,510,000 copies).

"Janson," as the book is usually referred to in theip, trade, has become the bible of the basic visual arts for contemporary students; it is now printed in 14 languages.

H.W. Janson was already thinking of a third edition at the time of his death in 1982. That version -- which weighs in at seven pounds and has expanded about 50 pages over the second edition -- finally hits the stores this month, significantly if not drastically altered. Under the editorship of Tony Janson, now 43 and chief curator of Sarasota, Fla.'s John and Mable Ringling Museum of Art, it has 824 large pages, 1,265 illustrations, 177 of them in splendid color, and costs $40.

Abrams' initial printing of 45,000 this time turned out to be inadequate. The original idea was to make this the "trade" printing just to get the book into the stores. Prentice-Hall was doing the textbook printings separately to meet the fall campus demand. But, unexpectedly, the new edition immediately became a bonus selection of the Literary Guild, more than selling out the first printing before publication date. "We've made the book clubs before," recalls Janson, "but never as a new book." So 9,000 "trade" copies had to be borrowed from Prentice-Hall.

The younger Janson, here to install the Ringling museum's lavish show of Baroque painting at the National Gallery, confesses that "Baroque is my first love" in art. His most conspicuous change in the text, however, involves not Baroque art but the addition of photography as an art form.

The elder Janson had opposed this, says his son, on grounds that "photography had not been treated in art historical terms, and that therefore the study of photography as part of art history was at a rather infantile stage. And that even the discussion of whether photography was art was such a debatable issue that he really didn't feel the need to sort of open the Pandora's box.

"And after doing this," says Janson, "I can see why. It was hard to take this subject that was hardly integrated at all even in selective aspects into the discipline of art history and somehow make it work within a survey book. At times I was beating my head against the wall.

"But I think I did a pretty good job. to deal with how photography is related to what is going on, not only in art, but in culture as a whole."

As to the basic question, Janson writes in the new edition: "In itself, of course, photography is simply a medium, like oil paint, or pastel, used to make art but having no inherent claim to being art. After all, what distinguishes an art from a craft is why, not how, it is done. But photography shares creativity with art because, by its very nature, its performance necessarily involves the imagination. Any photograph, even the casual snapshot, represents both an organization of experience and the record of a mental image. The subject and style of a photograph thus tell us about the photographer's inner and outer worlds. Furthermore, both art and photography participate in aspects of the same process of seek-and-find. The photographer may not realize what he responded to until after he sees the image that has been printed."

There is a 16-page chapter on 20th-century photography, plus other segments on earlier photography dropped into sections of 19th-century art, beginning with the pioneering collaboration in the 1830s between Joseph Niece'phore Nie'pce and Louis Jacques Mande' Daguerre.

The other substantive change in the new edition recognizes women artists for the first time in the mainstream history of art. In earlier editions, the most recent woman mentioned -- almost unbelievably -- was an anonymous ancient Greek vase painter. Introducing women was a change that the elder Janson had endorsed before his death. Perhaps the choice of artists identified with the past century was not all that difficult -- such figures as Mary Cassatt, Georgia O'Keeffe, Louise Nevelson or Helen Frankenthaler.

There were some trickier choices. For instance, there was Artemisia Gentileschi (1593-c. 1653), an important figure in the younger Janson's specialty, the Italian Baroque. Her father, Orazio Gentileschi, has come down to posterity as the more celebrated artist. But Janson's own research has shown her to have been a painter of considerable influence, so in the new edition she becomes the dominant of the two figures.

Janson introduces her in this almost apologetic way: "We have not encountered a woman artist since ancient Greece. This does not mean that there were none in the meantime. On the contrary, Pliny mentions in his 'Natural History' the names and describes the work of women artists in Greece and Rome, and there are records of women's accomplishments during the Middle Ages. We must remember that the vast majority of artists remained anonymous until the 'Late Gothic' period, so that works specifically by women have proved impossible to identify . . ."

There are significant incidental changes that affect the tone of the book. In the second edition, the senior Janson took the safe route in selecting his first color plate, chronologically -- the "black bull" from the paleolithic cave paintings at Lascaux in France.

The younger Janson has replaced it with a real shocker, a hyper-realist offshoot of Pop art by the contemporary sculptor John de Andrea called "The Artist and his Model. 1980." It is a graphically detailed life-size female nude sitting on a white platform with a sculpture of the artist seated on a chair next to her, with a bucket of paints on the floor beside him.

Janson admires the work greatly, but chose it as the lead work in the book primarily for the issues it raises.

Janson writes this explanation: "All art involves self-expression. Most of us are familiar with the famous Greek myth of the sculptor Pygmalion who carved such a beautiful statue of the nymph Galatea that he fell in love with it and embraced her when Venus made his sculpture come to life. Recently the myth has been given a fresh interpretation by John de Andrea that tells us a good deal about creativity by reversing the roles. Now it is the artist, lost in thought, who is oblivious to the statue's gaze. She is clearly based upon a real model rather than an ideal conception, and is still in the process of 'coming to life' as the artist has not finished painting her white legs. The illusion is so convincing that we wonder which figure is real and which one is dreaming of the other, the artist or the sculpture? De Andrea makes us realize that to the artist, the creative act is a labor of love that brings art to life."

Certainly, Janson agrees, some teachers will be turned off by the work. "Let them use another book," he says, adding, "I don't even agree myself with 100 percent of what's in the book. But I agree with about 90 percent."

Janson finds himself in particular disagreement with the way his father treated American art in the eras before Abstract Expressionism started in the '40s, causing even so eminent an artist as George Bellows to get less than his due.

"My father was a first-generation American," explains Janson. "And he was, like most first-generation Americans, so American it was unbelievable. It meant everything to him -- personally, professionally, spiritually. But he never was able to look at American art through American eyes. Now, I'm a second-generation American. It's really a matter of when you were born, and where -- and therefore what personal approach you bring to this book."

One aspect of the earlier editions that the new editor has gone out of his way not to trifle with is the tone of its writing. "The book is reasonably conversational," he notes. "It's important that it never become condescending to the artist or to the reader. Never be disrespectful to the art. Not everyone will like every piece in this book. And there will be some disagreements. But every piece in this book is a major work, and demands to be treated with that degree of respect."

Janson has also reached another conclusion about future editions: They should never exceed seven pounds. He learned that the hard way.

"Last month I was in New York doing some public relations work on the book. I was rushing out on a rainy day to meet someone for lunch, carrying the book in a briefcase. As I ran out of the building, I slipped on the wet pavement. I fell one way. And the book went the other way. I tried to catch myself, and my back slipped out of place. That could become a real problem."