Jean Paul Carlhian's latest designs for the visible parts of the Smithsonian Quadrangle--those huge new underground museums disguised on the surface as a couple of sedate little pavilions in a park--are exquisite in all respects.

And it is no accident that the drawings he submitted are in themselves just as fine as they can be. Delicate in outline and shaded just so, they might have won a prize a century ago: Carlhian was a student at the Ecole des Beaux Arts in Paris where, indeed, the act of putting pencil to paper with perfect results was taught as a fundamental principle of design.

As reproduced in an elegant new brochure, these renderings will provide no little help to Smithsonian secretary S. Dillon Ripley in his campaign to raise half of the estimated $75 million needed to pay for the project, which consists of the National Museum of African Art, a new center for Oriental art and numerous classrooms, meeting rooms, study spaces as well as offices for the Smithsonian Traveling Exhibition Service and Smithsonian Associate programs. Congress has authorized, although not yet appropriated, money to pay the other half of the bill.

There are faults in the design and in the overall plans for the project, but it should be said right out that it is an imaginative and much-needed plan--Ripley's last hurrah, some say. Although putting museums underground causes some problems, the location is apt symbolically and functionally. The buildings, 96 percent underground, will be dug three levels deep underneath a beautiful park bounded by the Smithsonian Castle, the Arts and Industries Building, the Freer Gallery and Independence Avenue.

Even before its acquisition by the Smithsonian four years ago, the Museum of African Art had outgrown its quarters in row houses on Capitol Hill. The new location on the Mall will do much to improve its stature as well as satisfy its need for more space. If properly managed, the center for Near Eastern and Asian art, which seems to change its name almost monthly, can be a splendid complement to the collections and programs of the adjacent, incomparable Freer. Furthermore, in Ripley's vision, the combined institutions can serve as a "window on the Mall" for non-Western cultures.

The recent designs, to be considered in coming weeks by the Fine Arts Commission and the National Capital Planning Commission, are a tremendous improvement upon awkward initial attempts to make each entrance pavilion a cultural symbol --pagoda-like for the Oriental institution, vaguely (and ineptly) "African" for its fraternal twin. In their new, Carlhian-inspired incarnations, the pavilions are sui generis--a little exotic, maybe, but culturally neutral.

Each building, a bit over 40 feet high, measures 90 by 60 feet and consists of six 30-foot-square bays. This simple grid is emphasized at the roof and along the exterior walls. Six copper-sheathed pyramid forms make up the top of the Oriental building; six identical domes top off the African structure. The bays along the granite walls are animated with beautifully proportioned niches and windows in the form of diamond-shaped arches for the Oriental structure and rounded arches for its companion.

Carlhian, who hangs his hat at the Shepley, Bulfinch, Richardson and Abbott firm in Boston, justifies his forms with references to the crazy-quilt architectural context that runs from picturesque 19th-century Gothic (James Renwick's castle) to vigorous Victorian polychromy (Cluss and Schultze's Arts and Industries building) to Renaissance revival elegance (Charles Platt's Freer), but such subtle, well-nigh invisible, allegiances are not terribly important.

In these two buildings Carlhian is playing an abstracted, Beaux Arts revival game, and what matters most are the harmonious proportions and fine details of the buildings, and the nice way they sit in the park. They will, I think, make a pretty pair, inside and out. The same cannot be said for his glass-enclosed entrance kiosk between the Freer and the castle, the dome of which has the ungainly exuberance of a Tokugawa warrior's helmet. (This is no minor distraction: From the Mall the kiosk, which will serve as an entranceway to the educational facilities, will be the most visible part of the project.)

The park itself is a treat that manages to preserve the primacy of the castle building in the ensemble (marked by a recreation of Renwick's original gateposts) while providing a restful enclave. On either side of the main axis leading to the castle there are two major focal points, each detailed with fountains, rivulets of water, handsome patterns of paving and flowers, bushes and trees.

It would be too much to say that the park brings back the spirit of Andrew Jackson Downing, whose informal "English garden" plantings graced the Mall a century ago, but its combination of formal and informal elements plays well against the Mall's Versailles symmetry. It is the setting of the park, more than anything else, that justifies Carlhian's concept of the entrance pavilions as exquisite jewels.

It remains to be seen, down under, whether the third-level corridor turns out to be an entrancing, skylit space, as intended, or a gloomy alley, as is possible. The exhibition spaces in the underground buildings are ample, though far from ideal, particularly on the second level where a ceiling height of nine feet is, to put it mildly, a bit tight for the purpose. But the entrance stairwells, skylit and open inside the pavilions, will make for a dramatic, welcoming descent.

The lack of a restaurant in the new building is a correctible flaw: One could be quite nicely fitted into a wing of the Arts and Industries Building, now a honeycomb of offices. A more subtle problem is the potentially competitive relationship between the institutions, particularly between the new Oriental center and the Freer, which, physically, will be linked by a passageway at the first underground level.

The protective idiosyncracies of Charles Lang Freer's great bequest--artworks in the Freer collection cannot leave the building, nor can they be supplemented with loans--created a need for a place to house temporary exhibitions of Oriental and Near Eastern art. The new center, however, also is envisaged as a collecting institution, a cause for some concern for anyone familiar with the Freer's renowned standards of quality and scholarship.

It is a good sign indeed that Dr. Thomas Lawton, director of the Freer, will become the head of the new institution, too, but nowhere is that policy etched in stone, or even printed on paper. Perhaps it should be.

But the happy story here is the way Carlhian's skill transformed an ugly duckling into quite a beautiful thing. It reminds me of the time recently when he was in Washington, speaking to a group of students and fellow professionals. "The main thing is to get on with it and to draw," Carlhian pronounced, lingering over that final infinitive as if it were the essence, the cardinal rule, the last word. The man cannot be faulted for not practicing well what he preaches.