When he was not busy fomenting the French Revolution, overturning the theory of education or generating hot material for his autobiography, Jean-Jacques Rousseau longed to be a musician. He succeeded in this more spectacularly than in most efforts of his lifetime, producing in 1752 a brief comic opera, "Le Devin du Village," which ran up some 400 performances in Paris alone before the end of the 18th century, had its New York premiere in 1790 and indirectly influenced Mozart's first operatic effort, "Bastien und Bastienne."

The show opened and closed a limited Washington run last night in the Folger Library's Elizabethan Theatre, and when it was over some of the audience could be heard humming tunes from it on their way out.

Strictly speaking, it was not "Le Devin du Village" that was presented last night but "The Cunning Man," an adaptation of Rousseau's material prepared for the London stage by the 18th-century historian of music, Dr. Charles Burney. The program notes explain carefully what musical changes are made by the great scholar, and one can't help feeling that the opera probably gained at least a little in the translation.

Of the 14 arias and duets in the show, two were composed (along with all the recitatives) by Burney, who was a competent if not an inspired musical craftsman, and they stand out sharply in the text. One is the soprano aria, "I'll tease him and fret him," reminiscent of Handel, and the other the baritone aria, "Some think in the stars we are able," which has moments that foreshadow the work of Gilbert and Sullivan. In the recitatives, too, Burney showed his own cunning; when the heroine sings, "Ah, me, I die!" she does it in exactly the cadences prescribed for such sentiments by the serious opera of the time.

Rousseau might not have liked these improvements; his own music has simple, melodious quality which may have been dictated by his limitations as a composer but also fit in with his philosophical theories. It also provided a healthy contrast to the over-elaborated forms of the period.

The simple comedy about a rustic couple ("nymph" and "swain" in the jargon of the time) whose love is first blighted and then aided by a fortune-teller who makes a profit on the deal, was very pleasingly presented by a small Boston ensemble, The Friends of Dr. Burney. Soprano Jeffifer Paterson had the most singing to do and did it with charm and style, ably abetted by baritone David Ripley and tenor Charles Walker.