The flamboyance of the Forstmann mansion, a Neo-Italian Renaissance palazzo piccolo built in the 1920s, has softened with time. By now, it is a relic of old New York, something to be honored and preserved, like the spoils of Poynton. Henry James might have loved it as a backdrop to his contest of sensibility among the refined Fleda Vetch, the coarse Mona Brigstock, and the imperious Mrs. Gereth, whose collector’s mania unfolds as a subtle species of vulgarity. In literature, such a test of character ends in purifying flames. In life, it ends as an art gallery.

The building did penance in the 1940s as a convent serving Catholic charities; it later became the Catholic Institute for the Blind. Since purchased and renovated by Salander-O’Reilly, it is regaining some of its original flavor. On exhibition is a collection of French paintings, landscapes from the late 18th century to the mid-19th.Works are offered in association with Galerie Lestranger, Paris, opened in 1994 by Catherine Sterling, daughter of art historian Charles Sterling.

These are small cabinet-size scenes of Italy and France that range in style from the Neoclassical to the Romantic. Many are by the students and contemporaries of Pierre-Henri de Valenciennes (1750-1819), an esteemed salon painter in his day. It is a delightful selection of lesser-known painters accented by a few luminaries: Corot, Delacroix, Courbet, Redon, and Theodore Rousseau. Slipped in under privilege of celebrity are a wan head of Christ (Redon), a stilted nude in an incongruous setting (Courbet), and a gem of historical anecdote (Delacroix).

Viewed against wainscoting, redflocked walls, antique chairs, and lighting dimmed to a votive candle, the exhibition signals a lifestyle. This is as much a reception as a display of work for sale. The paintings stand to receive your admiration, like debutantes at a cotillion. Anything short of applause and quick kisses down the line seems ungracious. Permitting issues of attribution even to enter your head is as impertinent as asking a girl how much her father is worth. But the issue is implicit in the accompanying catalog’s concern to address it.

Of the three dozen works here, fewer than half are dated and most do not bear signatures. (An inscription on an old label in the back is not a signature.) This is no bar to enjoyment, but it sharpens awareness of the intricacies of aesthetic judgments made in the context of a largely unregulated market. The critic is obligated to observe A.J.Ayers’s insistence on “an unbridgeable gap between the conclusions we desire to reach and the premises from which we set out.” As we know from Bernard Berenson’s collaboration with Joseph Duveen, connoisseurship can be a flexible premise.

Start with the newly rediscovered Valenciennes, whose reputation went into eclipse after 1840. Drawn to Rome like many French artists of his day, he worked out of doors and was a passionate voice for plein air painting. (An antique stage set of the plein air painter’s equipment is displayed in the gallery window.) His three unsigned entries here are undeniably lovely. “Study of a Tree” is a sublime oil drawing. But the six-figure price tags heighten your attention to other matters.

The catalog statement about one of these unsigned oils is instructive: “Similar to other works attributed to Valenciennes that recently appeared on the market, the present painting does not belong with the ordered catalog left by the artist. The proposed attribution is thus exclusively based upon stylistic comparisons.” Add to this the necessary caution over old works that lately have appeared on the market, and you have a clue to the hazards of what Robert Lacey, in his book on Sotheby’s, called bidding for class.

Subjectivity is again the basis for including the unsigned “Besancon” in the forthcoming supplement to Rousseau’s catalogue raisonne. Inclusion is less reassuring than it sounds. Such eminent authorities as Julius Meier-Graefe and Jacob Baart de la Faille, author of Van Gogh’s catalogue raisonne,were convinced of the authenticity of a score of Van Goghs unloaded on the market by a Berlin dealer from the 1920s onward. Attribution was later discredited.

The problematic role of subjectivity in assigning dates and attributions is evident in the catalog’s frequent use of such phrases as “very likely,” “may thus be datable,” “perhaps an evocation,” “we think that,” “suggests that,” and “is most likely.” A wonderful unsigned, undated Sicilian scene (“possibly” Monte Rosso) is listed as a work by Jean Briant. Only one other painting by Briant is known to exist. Confirmation of the authorship of the present canvas is based, according to the catalog, on “a mere intuition leading to comparisons that seem to confirm this hypothesis.” The asking price for this intuition is $140,000.

Of the (perhaps) three Corots,”Marino” (1826-27) is a powerful, finely detailed scan of light raking a steep Italian hillside. Another is a desultory oil sketch of Venice. The third is a slight, unsigned view of Roman rooftops that gives no indication of Corot’s mastery of the tonal structure of buildings.This is the only painting in the exhibition that takes the caution of prefacing the name of the artist with “Attributed to.” The phrase calls to mind Newsweek’s famous old quip that of the 2,500 paintings Corot made in his lifetime, 7,800 of them were in the U.S.

Two paintings must not be missed: Delacroix’s “Trees in a Hilly Landscape,” a delicate, lilting movement of color and sunlight; and Rousseau’s (signed) panoramic vista “Landscape Near Paris” (1829-31). The luminous haze that Baudelaire so admired in his work is magnificent here.

This is a deeply pleasurable show. Enjoy it.And on the way home, look for the essay collection on the problems of attribution edited by Mark Jones for the British Museum Press, 1992.

Until February 25 (22 E. 71st Street, 212-879-6606). Prices: $50,000-$750,000 (some prices by request only).