Handsome new museum needs equally handsome art. CANADA'S NATIONAL GALLERY

THREE things stand out after a leisurely stroll through the striking new home of the National Gallery of Canada, a spectacular glass building that opened in May: Its impressive and unique architecture.

The building's appropriateness for the display of art.

The wide-ranging nature of the gallery's collection, and the fact that it includes a number of superb and important pieces.

That said, one can't help but note a discrepancy between the imaginative grandeur of Moshe Safdie's new structure and the overall quality of the art it contains. The National Gallery's architecture proclaims it to be a world-class museum, but its collection doesn't yet quite live up to that claim. But then, that should come as no surprise, for this museum obviously was built as much to house what the National Gallery expects to acquire as what it already owns.

The art is exhibited on the second and third levels, in galleries divided into the following categories: Canadian; contemporary; European and American; Asian; Inuit; prints and drawings, photographs; and special exhibitions.

The Canadian Galleries provide some of the most pleasant surprises to a visitor from the United States - both in the historical area (particularly 1870-1930), and among the paintings and sculptures produced during the past three decades.

Even a quick visit to these galleries will prove rewarding to those not familiar with Canadian art, for they contain many excellent examples by the best of the early pioneers. Among them: Tom Thomson's ``The Jack Pine'' (1916-17), the paintings of the Group of Seven (founded in 1920 to establish a truly indigenous Canadian art); and the striking images of Emily Carr, most notably her dramatically mythic ``Blunden Harbour.''

As impressive as any room in the ``contemporary art'' section is the one devoted to a handful of huge abstract canvases by Canadians who explored the formal and expansive properties of color and pictorial space. These flat, extremely high-keyed and sparse paintings by Charles Gagnon, Yves Gaucher, and others create an atmosphere that communicates exactly what these artists were trying to do.

On the other hand, such US painters as Warhol, Flavin, Rosenquist, Segal, and Lichtenstein, are represented by works that are more typical than outstanding.

Remarkably effective, if occasionally rather self-consciously so, are a number of large wall and three-dimensional pieces assembled to explore the variety found in installation art.

These, in turn, lead the viewer to the European and American galleries, and to such relatively recent works as Francis Bacon's ``Study for Portrait No. 1,'' Leger's ``The Mechanic,'' Pollock's ``No. 29,'' and a tiny but stunning 1910-11 Cubist oil by Braque. From them it is only a short step to a grouping of fair to first-rate works by such masters as C'ezanne, Monet, Pissarro, Degas, Van Gogh, Matisse, and Picasso.

It is when we get to the rooms devoted to the major periods of Western art that the Gallery's main strengths and weaknesses become most apparent. Great masterpieces abound - but so do relatively minor works, and in sufficient quantity to weaken some of the positive effects of the greats. This undoubtedly will be rectified, and fairly soon, depending of course on the generosity of everyone concerned and the availability of important works on the market.

Simone Martini's ``St. Catherine of Alexandria,'' executed in the early 1320s, is the oldest Western masterpiece on view. It holds up beautifully in the company of Benozzo Gozzoli's ``Virgin and Child with Saints,'' and Piero di Cosimo's famous ``Vulcan and Aeolus'' - which was painted between 1485 and 1490 and proves that creative idiosyncrasy is not a modern phenomenon.

From then on, things become quite lively, with good to superb examples by, among others, Cranach, Veronese, El Greco, Poussin, van Dyck, Canaletto, Rembrandt, and Jordaens.

Rubens's brilliantly personalized copy of Caravaggio's ``The Entombment,'' is about as magnificent a piece of painting as one can find anywhere. And Simon Vouet's ``The Fortune Teller,'' although not on the same level, commands respect.

Also outstanding are Constable's ``Salisbury Cathedral From the Bishop's Grounds,'' Turner's luminous ``Mercury and Argus,'' and, of course, Benjamin West's historical icon, ``The Death of General Wolfe.''

Mention should also be made of excellent pieces by 20th-century English artists, especially Henry Moore, Stanley Spencer, and Augustus John, as well as impressive canvases by Canadians Jean-Paul Riopelle and Alex Colville.