Consistency of vision makes this collection an artistic feast

Art collectors are a mixed lot. Some buy everything they can lay their hands on. Others buy only what is fashionable. And others still view the collecting of art as nothing but a pleasant form of investment.

There is another, much rarer type of art collector, however. This kind genuinely loves art, understands and respects what it represents, and buys it not only for enjoyment but also to express confidence in a particular artist or movement. These collectors are often among the very first to see the quality and importance of new talent and new ideas - and among the very first to fork over their hard-earned cash (not all collectors are wealthy) for work that almost everyone else sees as worthless. They are often, as a result, at the cutting edge of new art movements, and as instrumental in giving credence to brand new art as the more perceptive dealers, critics, and curators.

Among the most dedicated and intelligent of these collectors are Emily and Burton Tremaine. Their collection of modernist art not only contains some of the best art of the century, it also comes very close to being a work of art in itself (in the relationship of the works to each other).

Now, the public can decide for itself at the Wadsworth Atheneum's beautiful and impressive showing of the Tremaine Collection here. On view are 147 paintings, sculptures, drawings, and prints. The earliest, a Robert Delaunay painting, is dated 1912, and the most recent, a Mel Kendrick sculpture, dates from 1983.

The tone of the Collection is set by a handful of extraordinary works: Robert Delaunay's ''Premiere Disque''; Fernand Leger's ''Le Petit Dejeuner''; Georges Braque's ''The Black Rose'' (Mrs. Tremaine's first serious purchase); Piet Mondrian's ''Victory Boogie-Woogie'' (the artist's last painting, and almost certainly the most important modernist painting still in private hands); Jackson Pollock's ''Frieze''; Jasper Johns's ''Three Flags''; Robert Rauschenberg's ''Windward''; and Frank Stella's ''Luis Miguel Dominguin.''

But that is only the tip of the iceberg. Few major modernists are excluded from this collection, and those that are missing are generally missing by choice rather than from necessity. One will look in vain, for instance, for examples by the German or Austrian Expressionists (or by any of the recent Neo-Expressionists, for that matter). Neither are Surrealism, Op-Art, Color-Field painting, or Photo-Realism represented at all or in depth. One will also be disappointed if one expects to find work by such ''eccentrics'' as Francis Bacon or Stanley Spencer.

But no matter, this is a personal collection: an outward expression of an ideal that was carefully and thoughtfully shaped over nearly 50 years. That is the real beauty and significance of this collection.

In its clarity and consistency of vision, its unification of individual physical objects into a symbol of modernist formal and spiritual ideals, the collection not only remains true to the intentions of modernism's greatest heroes but actually places itself in their company.

If this collection is a work of art, then the staff of the Wadsworth Atheneum has ''framed'' it beautifully. From Klee, Miro, Picasso, and Giacometti to Irwin , Zakanitch, Marden, and Valenta, everything has been positioned for greatest effectiveness. Even such tiny items as Johns's exquisite ''Grey Numbers'' and Marden's ''Marble 14'' are permitted to hold their own among much larger works. And Barnett Newman's ''Outcry'' and 'The Moment II'' will probably never look better than they do hanging side by side on one large wall.

There is an overall aura of balance and thoughtfulness in this collection that can only be described as classical, and that results from the Tremaines' preference for the formally resolved over the formally tentative. Even such profoundly instinctual and ''eruptive'' artists as Pollock, Miro, Giacometti, Appel, Kline, and de Kooning are represented by exceptionally solid - even almost serene - examples of their work. And the Pop Artists included seem unusually measured in the works by which they are represented.

Only one major work on view seems somewhat at odds with this ''classical'' aesthetic: Roberto Matta's somewhat ''busy'' and convoluted ''Splitting the Ergo.'' Its inclusion, however, is a fascinating one, for it throws into clear relief the high-minded seriousness and formal unity of the collection.

The Tremaines see collecting as a dynamic commitment. They have always been more concerned with what was emerging than with what was already formed. Thus, it is easy to see why they responded so strongly to Pop Art (Mrs. Tremaine described it as ''a comet that flashed across this dark scene with a blazing light and we saw objects we really had never seen before'').

The end result is one of the most important post-World War II collections of modernist art - and convincing proof that modernism has been and is one of mankind's most noble creative efforts.

At the Wadsworth Atheneum, 600 Main Street, Hartford, Conn., through May 8.