We all should have such birthdays. The Virginia Museum of Fine Arts, fast approaching 50 and all dressed up for the occasion, this week will unwrap the presents it's received -- four separate collections and a new West Wing to house them. The 2,000 objects in it, and $12 million too, are gifts to the museum from four generous Virginians, Sydney and Frances Lewis and Paul and Bunny Mellon. We all should have such friends.

Mellon's art philanthropies have always expressed not just his taste and tact, but the tuggings of his heart, for he is sure of his affections and his loyalties are strong. He is loyal to his prep school. His gifts to Choate include a center for the arts designed by I.M. Pei. He is loyal to his college. Perhaps his finest benefaction is the wonderful museum, designed by Louis Kahn and filled with British pictures, that he has given Yale. He is loyal to his nation, too, and to his father's memory, debts he has retired by his many years of service, and his many gifts, to the National Gallery of Art. (Paul Mellon and his sister and their family foundations spent nearly $100 million on I.M. Pei's East Building there.) Nor has he forgotten how much he owes Virginia, his adopted state.

From Paul and Bunny Mellon, Richmond has received two distinctive art collections, one of English sporting pictures and another of French paintings. Bunny Mellon is devoted to gardening and growing things and French pictures one can live with, and one sees that here. Among her husband's deepest pleasures are those that he has taken from the hunt country near Upperville, from the soft mists on the Blue Ridge on autumn afternoons, from the sight of well-bred horses, the sounding of the horn and the pealing of the hounds. Mellon's sporting pictures, with their meticulous portrayals of foxes, dogs and horses, are not to everybody's taste. Some are rather homely. But they reveal what he loves.

The gifts to the museum from Sydney and Frances Lewis are comparably heartfelt -- and even more impressive. The Lewises, the founders of the Richmond-based Best Products Co., have formed two grand collections, both of which have now been given to their state. One, of late 19th- and early 20th-century decorative arts, may well be the finest -- it is surely the least expected -- of the many gifts given the museum. It includes tables, chairs and sofas, stained-glass lamps and windows, jewelry and statuettes, in Art Nouveau and Art Deco and associated styles. Few museums anywhere could begin to match it, for its quality is awesome and its range is wide.

"We are crazy, mad collectors," says Frances Lewis. Their second art collection -- with its Oldenburgs and Warhols, Schnabels, Lichtensteins and Gilliams -- is bold and bright and jazzy, and sure to please the crowds. Its 600 objects survey much of the best art made since World War II.

The gifts in the West Wing were not coldly purchased. Warmth surrounds them all. The Lewises at one time wrote letters at that desk, they slept in that grand bed. Those small and strangely touching pictures of the hunt have come from Mellon's home. The Virginia Museum of Fine Arts -- with its European tapestries and paintings, its Indian temple sculptures, its pre-Columbian, Nepalese and African collections, its Greek red-figured vases and its Roman marbles -- is encyclopedic. It likes to think itself a sort of mini-Met.

Its limestone-clad new building will be dedicated Tuesday with the governor presiding, for the Richmond institution is owned wholly by the state. One expects from state museums a sort of bureaucratic caution, a touching of all bases and a kind of patient lecturing. But nothing of the sort is experienced by the visitor to the new West Wing. Its four collections differ greatly, yet they share the building happily. The one quality they share is how personal they feel.

The museum has spent years carefully preparing for its golden aniversary. Its original small building, a neo-Georgian structure of moderate distinction that opened to the public in January 1936, has been gracefully refurbished. Cost: $900,000. Its walls have been repainted (with pleasing colors chosen by Hugh Newell Jacobsen), its objects have been reinstalled, its roof has been repaired, and skylights closed for years have been opened.

Under Paul N. Perrot's spirited direction, the Virginia Museum, a once-weak institution, has been climbing toward the big leagues. It now is almost there.

The 90,000-square-foot West Wing, designed by Malcolm Holzman of Hardy Holzman Pfeiffer Associates, doubles the museum's exhibition space. It cost $22 million, though more than that was raised. The round sum of $10 million was provided by the state, an additional $3 million was raised by the museum, and the Lewises gave $6 million, as did the Mellons -- which leaves $3 million for an acquisitions fund.

Richmond is a quiet place, conscious of its history and conservative in spirit. Holzman sensed that clearly. His building is polite. It neither thrills nor jars.

Though Holzman has designed Best Products' Richmond headquarters (the building won an AIA Honor Award in 1983), his West Wing may be seen as a slight bow to the Mellons, for it distantly suggests both the East and the West Buildings of the National Gallery of Art.

Holzman's building, from the outside, recalls John Russell Pope's. Its subtly striped fac,ades, at least for the most part, are windowless and flat, weighty in their stoniness, delicate in their details and classical in mood. Like those of Pope's West Building, they seem to tell the onlooker this structure is a treasure chest, there are valuables herein.

But Holzman's building, from the inside, evokes I.M. Pei's. For it, too, has a central hall that is less a place for art than an "orientation space" with balconies and bridges, wide, imposing stairs, tall walls clad in marble and skylights high above.

The viewer won't get lost there. The Mellons' two collections are installed to the left, the Lewises' to the right.

Paul Mellon has been working for American museums for nearly half a century, but not as a collector. Though he supervised the construction of the National Gallery's West Building in the 1930s, and though he was first appointed a trustee of the Virginia museum 45 years ago, he began buying art in earnest relatively late.

His ties to the museum played a role in his decision. The catalyst that helped make him a collector was an exhibition held there in 1960 called "Sport and the Horse." Though Mellon at the time knew little about English art, he knew plenty about horses, and when asked to head the selection committee for the exhibition, he did not refuse. In the course of his involvement, a passion was ignited. Some of its results are now there on view.

The 58 sporting paintings he has given to Virginia are, with some exceptions, not the best he's purchased. The best belong to Yale, or are still in Mellon's homes. Of those displayed in Richmond, many are but middling. The group, writes Judy Egerton, author of the catalogue, "accurately reflects the average level of pictures by sporting and animal artists of the period 1700 to 1850." "Average" is a word not often tied to Mellon. These English sporting pictures, although compelling records of British country life, need not be overpraised.

Still, some are splendid objects. John Wootton's "A Bay Horse Led Towards a Rubbing-Down House at Newmarket" (circa 1715) is among the most impressive. George Stubbs' sniffing spaniel of 1773 is also very fine. Others are endearing -- W.J. Pringle's "A Sportsman Talking to His Beater After Coursing" is particularly charming -- and many are amusing, for instance, Philip Reinagle's portrait of a piano-playing spaniel. These objects speak to tastes more easily acquired in the hunt country of Virginia than in other regions. If you love the sporting life you will love them all. If you don't you won't.

The 69 French paintings given by the Mellons by no means include all the grandest they have owned. True, the Degas are terrific, so is the Ce'zanne. The 1905 Picasso, "Jester on Horseback," is a first-rate picture, too, as is the horse by Delacroix and the landscape by Vuillard. But Paul and Bunny Mellon have not stripped their homes. They retain many masterworks by van Gogh and Ce'zanne and other major painters, "paintings," writes John Walker, the National Gallery's director emeritus, that "in all probability will ultimately rest in the National Gallery of Art."

The Lewises, in contrast, are less closely tied than Mellon is to other institutions. One gathers from their gifts that they have focused their commitments on the Virginia Museum of Fine Arts. Most curators of modern art -- those, for instance, at the Hirshhorn -- would give their eye teeth for the best new things in Richmond. Among the most imposing are that giant Anselm Kiefer and the huge portrait by Chuck Close. Julian Schnabel, Susan Rothenberg, Red Grooms, Brice Marden, Gilbert and George, Deborah Butterfield and many other artists now very much in vogue are well represented, too.

And any museum anywhere would be enormously enriched by the Lewises' collection of decorative arts.

They have given the museum some 600 splendid objects. Peter Behrens, Frank Lloyd Wright, Bugatti, Hector Guimard, Louis Majorelle, Gerrit Rietveld, Otto Wagner, Josef Hofmann, Emile Galle' and Charles Rennie Mackintosh are among the designers whose works they have collected. There are statues here by Alphonse Mucha and more than 100 works of art in glass by Tiffany. Though many later modern artists scorned rare woods and stained glass, ornament and inlays, those represented here reveled in such luxuries. Their handiwork suggests Versailles more than it does Conran's. The decorative arts collection the Lewises have formed will not soon be equaled, much less surpassed. By itself it justifies a trip to the West Wing.

There will be parties there all week. A party for the construction workers and the museum's immediate neighbors will take place today. A luncheon and a gala ball will be held there Tuesday. The Council of the Virginia museum will have a tea there Friday. Two days of "celebratory festivities," paid for by Philip Morris, which has also given the endowment $500,000, have been scheduled for next Saturday and Sunday. The whole Richmond community is invited. The openings will end sometime Sunday night following a concert by composer Philip Glass. The museum will be closed Monday, Dec. 9, for a much needed day of rest. When it reopens Dec. 10, its new West Wing will be open to everybody else.