During the baroque 18th century, nationalistic distinctions in music were proudly nurtured. English music tended to be companionable; the Italian, brilliant; and the French, formal, carefully premeditated and highly mannered but not without wit.

Reconstructing the style that is only hinted at in French scores is a sport pursued by numerous ensembles, but none has managed to make this style sound more natural and idiomatic than the Kuijken Quartet that performed at the Smithsonian's Hall of Musical Instruments last night.

Bart Kuijken plays a one-keyed flute that has the sort of mellowed sound one might associate with fine wine or well-ripened cheese. Sigiswald Kuijken has a graceful but incisive way with his 17th-century violin, and the third brother, Wieland, plays a very solid but sympathetic bass viol. The harpsichord backbone, occasionally more subdued than necessary, was provided by Robert Kohnen.

Couperin, Rameau, Leclair, and Hotteterre were welcome and familiar names on the program, but two unknowns provided the greatest interest. A Trio Sonata by Mondonville proved to be an example of almost disembodied, purely distilled French baroque mannerisms, and a "concert" for two viols called "Le Tombeau" was a gem of a tiny programatic soap opera dealing with death and eternal bliss.