The Smithsonian's new Smithson String Quartet, which practices the art of late 18th-century chamber music on instruments tailored to the specifications of Mozart's, Haydn's and Boccherini's day, played a lovely concert of works by those three composers last night at the Hall of Musical Instruments at the National Museum of American History.

This period style--with its gut strings, short bows etc.--is not all that different from the brilliant, more resonant string sounds that have prevailed for roughly the last two centuries. Basically, what these instruments produce are smaller, sweeter sounds.

The argument for the 18th-century style is that one is hearing the music as the composers probably heard it; the argument to the contrary is that a large, deeply felt work like last night's Haydn C Major Quartet, Op. 54, No. 2, loses some of the breadth and grandeur that one hears when played with today's trimmings.

This Haydn quartet is just a step behind Beethoven in scope. Would one think of doing Beethoven in this style? It's beside the point. The Haydn quartet works in either style.

The quartet directly presages Beethoven in two specific respects. One is the haunting, almost free-form obbligato in the slow movement that the violin weaves uneasily over the measured calm of the other instruments in their little hymn. It is the kind of passage that became characteristic of the Beethoven quartets. Also there was the transformation of the last movement into what is basically a second slow movement. The tenderness of last night's playing made up for its occasional tonal roughness.

There was also a Boccherini oboe quintet, with oboist James Caldwell, which consisted of two relatively slow movments--a lovely work, with a captivatingly tender melancholy. Caldwell played on a period oboe that produced a richer sound than the modern instrument.

Mozart's compact little Quartet, K. 169, opened the evening.