The 42nd annual National Folk Festival at Wolf Trap, which concluded yesterday afternoon, should not be confused with the concert held at the amphitheater last night. The former was a joyous celebration of American musical craftsmanship. The latter was, for the most part, a dreary affair, filled with excesses of pop cuteness and mass-market mumbo jumbo.

The headliner, Noel Paul (as in Peter, Paul, and Mary) Stookey proved to be a skilled performer but to no particular purpose. His set ran the gamut from born-again Christian ditties to gospel-tinged ballads, all of which were presented in such a polished manner that any emotions were hidden beneath the gloss. The show was saved, momentarily, by a performance of "Puff (The Magic Dragon)" which touched more than one nostalgic nerve.

Singer David Mallett preceded Stookey with an undistinguished collection of songs that borrowed from various fold artists. Mallett has a strong voice and a sure melodic sense but much of his material sounded like an improbable cross between early Dylan and John Denver.

The concert would have been utterly banal were it not for the efforts of the Seldom Scene. This fine bluegrass group added touches of realness and gut human feelings which were seldom heard during the rest of the show.