"Are we going to hear Roberta Peters?" asked a woman in the waiting line at the Carter Barron box office. "I thought we were going to hear Beverly Sills."

It was indeed Roberta Peters, who celebrated her 50th birthday a few months ago and whose name was magic 20 years ago, singing in a concert postponed from a week ago. The posters outside Carter Barron gave that much information if no more. They announced her name and mentioned (rather vaguely) the Metropolitan Opera, where she made her debut in 1950, but they said nothing, really, about what would be going on.

"That's Harry Ellis Dickson," said a member of the audience, surprised and excited, as the conductor walked on stage to direct The Grand Carter Barron Philharmonic Pops Symphony Orchestra. Nothing had prepared the man for the appearance of the esteemed assistant conductor of the Boston Pops, whose name appeared neither on the posters nor on the program -- a pitifully small, fuzzily photocopied single sheet of paper. For all that the program revealed, Peters might have been conducting as well as singing.

If it had not been kept such a closely guarded secret that Arthur Fiedler's longtime associate would be in town conducting the kind of program that made the Boston Pops world-famous, the amphitheater -- an ideal place for concerts, an easy-to-reach, urban Wolf Trap -- might have been more than 20 percent full. There should have been a capacity crowd, but the promotion of classical concerts is a special art that the Park Service has not yet learned after 30 years of running Carter Barron -- though it has managed to attract people who can do it at Wolf Trap and the Kennedy Center. It will probably be said after the current series of pops concerts that classical music doesn't work at Carter Barron. That's not the problem: it should work, but it was pitifully mishandled.

The program itself was a handful of trumps from the opening Sousa march to the concluding "Boogie-Woogie Bugle Boy," including such sure-fire winners as Offenbach's "Orpheus" Overture, Bizet's "Carmen" Suite and Strauss' "Voices of Spring" as well as a series of arias sung by Peters. The new Carter Barron orchestra turned out to be a collection of some of Washington's top free-lance musicians.

In the case of Peters, the enthusiasm was somewhat overdone.Her voice is still fine at its best, particularly in the lower and middle registers, but the coloratura is no longer reliable and the top tends to be both thin and wobbly. At this point in her career, these facts are hardly a secret to music lovers, but Peters was only part of the program. By choosing to publicize her rather than a surefire program and conductor, the Carter Baron management deprived itself of a large potential audience and many Washingtonians of an enjoyable evening.