Actors Byrne Piven, Jeff Perry and Dick Cusack perform a small but very effective tour de force in the three-person play, "The Man in 605" by Alan Gross, and their achievement is likely to go relatively unnoticed because it happens tonight on FM raido outside of prime time -- to be precise, on WAMU-FM at 11 p.m.

When it is done right -- as it is in this installment of National Public Radio's imaginative "Earplay" series -- radio drama has special challenges and special rewards. All the players have to work with is their voices and a few sound effects, the evocative power of the spoken work and -- most important of all -- the listener's imagination, which can be more satisfying than the sets in a video drama if it is properly stimulated.

It all works together neatly in "The Man in 605," a carefully consructed drama about an aging poet (Piven), who was once great and is now sinking slowly into a haze of alcohol in a sleazy Greenwich Village hotel.

Perry is a young writer who has came to New York from the Midwest and taken a night bellhop job because he needs the money. His veneration for the old poet contrasts sharply with the sordid current reality -- and also with the hard-nosed attitude of the night manager (Cusack), to whom the man in 605 is "a bum."

Whatever he may have been, he is, in fact, now a bum -- though the shattered fragments of a great talent can still be found in him. Subtle three-way interactions between the sharply contrasted characters build slowly to a climax in which the young man is caught smuggling liquor to the tenant and faces the loss of both his job and his idealistic illusions.

Three expert characterizations, a fine evocation of Village atmosphere and a well-woven plot make this drama worth an hour of listening without a picture to watch.