For connoisseur or beginner, the city is an art viewer's feast

New York takes art very seriously. But why shouldn't it? No other city has as many museums, art galleries, auction houses, art schools, publishers of art books, and practicing artists.

One of the world's greatest museums, the Metropolitan, stands within easy walking distance of six other superb and important museums. And along one block alone - West 57th Street between Fifth and Sixth Avenues - dozens of the best galleries in America exhibit some of the best art being produced today.

But that's not all. Scattered throughout Manhattan and the four other boroughs are numerous other excellent museums of all sorts and sizes, hundreds of commercial galleries, and cooperative and subsidized establishments that show the latest and most experimental art, often with very little hope of selling it.

New York, in short, is very art-conscious - to a certain extent, I suspect, because art is now big business, but also because New Yorkers have learned to appreciate it.

That appreciation is shared by an increasing number of out-of-towners visiting the city. Unlike the native New Yorker, however, who can visit galleries and museums at his leisure, these individuals must choose what they want to see in the short time available to them.

It matters, of course, whether one's interest is casual or serious. If casual , a day or two in the major museums and a stroll among the galleries of SoHo (below Greenwich Village in the lower midtown area), upper Madison Avenue, and 57th Street should suffice. As a matter of fact, I recommend this for those visiting New York for the first time. It's an excellent and very pleasant way to familiarize oneself with what this city has to offer and to pinpoint areas to be explored in greater detail on future visits.

For those with deeper interests or with more time, however, I suggest a bit of planning. New York has roughly 80 art museums and exhibition spaces, and almost 500 art galleries - of which at least 200 are worth visiting. To avoid confusion, it's best to know what this city has to offer, and to plan an informal itinerary.

Two handy guides should help: ''A Guide to New York City Museums'' and ''Gallery Guide.'' The former gives brief descriptions of New York's 157 museums , and the latter lists the scheduled monthly exhibitions of roughly 350 of the city's galleries. A check for $2 to Cultural Assistance Center Inc., 330 West 42 nd Street, N.Y. 10036, will bring the former. ''Gallery Guide'' can be obtained for $3 from Art Now Inc., 144 North 14th Street, Kenilworth, N.J. 07033. When ordering, indicate which month the trip to New York is planned.

It helps a visitor to realize that art in New York is fairly equally divided between the art of the past and of the present. In no other American city can one get so complete a picture both of the US cultural heritage and of what is just emerging. Only here can one realize fully how extraordinarily alive, innovative, and diverse today's art really is. Other American cities have great museums and excellent galleries, but none other has so many of both.

There is the Metropolitan Museum, which is so huge and so full of the art of all places and periods that it would take weeks to see it all. Among its holdings are many of the very greatest works of art ever created, as well as works only recently completed. If I were new to New York and only had one day to devote to art, I'd spend it in the Metropolitan.

If, on the other hand, I only had two hours, I'd get over to the Frick Collection as quickly as possible. This former mansion of industrialist Henry Clay Frick contains only 169 paintings, but every one is of such high quality - and some are so breathtakingly great - that those two hours would be perfectly and unforgettably spent.

If a beautiful location is important, I recommend the Cloisters. Although considerably farther north than the other museums, its magnificent view of the Hudson River and its world-famous collection of medieval art and architecture make the short trip up to Fort Tryon Park more than worthwhile. The Cloisters houses the Metropolitan Museum's collection of medieval art, and is itself a composite of parts from five medieval monasteries, a 12th-century chapter house, a Romanesque chapel, and a 12th-century Spanish apse.

For those whose tastes run more to recent art, the Guggenheim Museum, the Museum of Modern Art, and the Whitney Museum offer as broad a selection of contemporary art as can be found anywhere. And the Brooklyn Museum, only a short subway ride away, often provides excellent samplings of what the art world is currently up to. The visitor should keep in mind, however, that the Museum of Modern Art is still operating at less than full capacity because of its building program, and that the Whitney exhibits only American art.

For a true picture of what is really happening in art, however, one must go to the galleries - and to as many of them as possible. That is where the real ''action'' is, where the various new and old ideas and forms jostle for position and for the attention of the art professionals and the public. The museums, after all, are limited in what they can show, and even the best of their new-talent exhibitions are selected by curators with very definite ideas on what is and what is not art.

When all is said and done, it's New York's many galleries that really set it apart from all other American art centers. For better or worse (and I'm quite willing to accept the possibility that it could be for the worse), what is shown in New York's SoHo, NoHo (just above SoHo), and Tribeca, on 57th Street and Madison Avenue, constitutes a good 90 percent of what the United States and the world perceive as American art.

New York's gallery world may not represent the grass roots of American art, but it is where most American art is ''packaged,'' exhibited, and sold. It may offend some that art here is such a high-powered, commercial enterprise, and that it occasionally forgets its cultural responsibilities in order to attract sales or fame. But that isn't all there is to the New York gallery world. Many dealers genuinely care about art, and some are as passionately and deeply devoted to it as any artist.

To discover this, however, one must visit as many galleries as possible, and in as many areas of the city as possible. Although the ''new'' and ''advanced'' in art are more likely to be found in a SoHo or Tribeca (an area south of SoHo) gallery, it can also be found in a little gallery on upper Madison Avenue or along 57th Street - and often for a very reasonable price.

New York is a great place to hunt for and to find art, to view some of the most magnificent masterpieces, and to get at least a rough idea of what is really going on in art today.

But New York is also a great place to buy art. It may take a little looking and walking, but it will be worth it. I can think of no better or more appropriate souvenir of New York than an original work of art - be it a tiny etching, an oil painting, or a sketch someone made of Central Park.