MUS'EE D'ORSAY. Paris turns a majestic old railroad station into a spectacular museum

AT last the French Impressionist painters have a spacious new home for their works, perfectly suited in style and atmosphere to the time in which they painted. After six years of construction work, the Gare d'Orsay, a turn-of-the-century railroad station and hotel situated along the Seine opposite the Louvre, reopened its doors last week as the Mus'ee d'Orsay, an institution devoted to the art of the second half of the 19th century.

It's not likely the Impressionists would have objected to their new quarters. Trains and stations provided subjects for Monet, Pissarro, and Manet. In fact, by a neat stroke of fortune, one of Monet's paintings of the French capital's Gare St. Lazare is part of the Louvre's remarkable collection of Impressionist works. It is this collection (among many other things from other places) that has been moved from impossibly cramped conditions in the Jeu de Paume into the Mus'ee d'Orsay.

To look at it across the river - the exterior of Victor Laloux's 1900 building has been cleaned up but is structurally unaltered - you wouldn't immediately guess that it is largely constructed of iron. That is because Laloux was forced by contemporary criticism to make a compromise. The lengthy fa,cade, along the building's main axis and running parallel to the river - a procession of arches between two enormous clocks - is clothed in stone and topped with elaborate statuary. Even the great iron vault which spans the ``Grand Nave'' inside is almost entirely hidden from the outside by traditional slate roofing.

Such disguise presumably satisfied those who feared that too much naked metal would be an affront to the glories of the Tuileries and the Louvre on the opposite bank. It also had the effect of making the station look almost like a palace - or an art museum. So it now might be said that for the first time its reason for being has caught up with its physical appearance.

It is so impressive, in fact, that - with the visitor's first sight inside, looking down and along the vast nave - it takes some time to adjust to the fact that the building's purpose is no longer to make rail travel look heroic. In re-creating the space, the Italian architect Gae Aulenti (also responsible for the galleries to house the National Museum of Modern Art inside the Pompidou Center and for turning Venice's Palazzo Grassi into an art gallery), together with architects of the firm ACT, have endeavored to strike their own kind of compromise-cum-confrontation.

Ms. Aulenti thinks of her work as a contrast to Laloux's. She treated the station simply as ``a box where all was possible.'' Nevertheless she, like Laloux, seems to have been well aware of the prestigious character of this revamped monument. She has resorted to her own more than generous use of stone as the principal material of transformation. Screens and walls and plinths and panels and walkways and even broom-closet doors are clothed in stone.

The nave itself (the setting chosen for a display of eclectic academic sculpture, much of which has not been seen in public since the 19th century) is walled along both sides with smooth but massive masonry partitions mildly suggestive of battlements. But the largesse of Laloux's space can take it, and Aulenti has used her not-exactly-modern stonework both as a way of massively consolidating the permanence of her reorganization and, more important, of humanizing it.

The tremendous variety of spaces not only allows for a number of big academic paintings and Courbet's great masterpieces (``The Painter's Studio'' and ``A Burial at Ornans'') to be shown with the grandeur they demand, but for much smaller works (Daumier's marvelous, small caricature-sculptures for example, and many decorative objects of the period) to be given appropriately scaled-down accommodation. The lighting ranges from the dispersed, open space of the nave, to the clear and bright upper galleries, where most of the Impressionists are hung, to shadowy spaces for drawings, photographs, and prints.

Aulenti has produced an intriguing, sometimes disorienting sequence of galleries on three levels. Laloux is never obliterated, and pops up unexpectedly all over the place with his iron girders and arches and columns. With varying degrees of success his 1980s successor has managed to contrive galleries (as well as audio-visual rooms, an auditorium and eating places, etc.) that are ``a suitable haven for contemplation.'' It is impossible any longer to imagine the noisy invasion of trains.

And what about the glories of the collections? They come from various sources: the former Mus'ee d'Art Moderne at the Palais de Tokyo; the Louvre itself; loans to provincial museums; the Mus'ee des Arts Decoratifs; from donations and legacies; from works offered in payment of inheritance tax; and from an active purchasing campaign started in 1978.

In their new setting, the Impressionists and Post Impressionists are not thrown in willy-nilly with the academic works of the time - the newer painters were shunned then and forced to be separate, so a continuing separation seems apt - but they are put in their context. Chronologically their emergence in French art can be traced; they can be compared with the contemporaries they were in rebellion against; and they can be seen as the forerunners of such artists as Seurat, Gauguin, Toulouse-Lautrec, and Bonnard.

The collections are remarkable and enormous, but spotty. While there are superb works by Seurat, for instance, one longs for more. The representation of non-French artists is incredibly thin - even those, like Munch, who lived and worked in Paris. In the decorative arts, again, there are striking imbalances in the pleasantly displayed art nouveau section. Even in the face of the superb Impressionist collection, it cannot be forgotten that the French state turned down numerous works left to it while still in the grips of an anti-Impressionist art establishment.

But this is to carp. You only have to circumnavigate the Cezanne or Van Gogh galleries, or peer into the case full of Degas sculptures, or find Manet's ``Olympia,'' or explore gallery after gallery of academic Salon pictures, to realize that this museum-in-a-railroad-station is more than a delight - it's a necessity.