The sex farce "Romancero Secreto de un Castro Varon" ("Secret Tales of a Chaste Gentleman") is being presented in its original language by the Grupo de Artistas Latinoamericanos at the G.A.L.A. Theater through the end of May. If you understand Spanish, this is one not to miss.

The play by Antonio Martinez Ballesteros is loud with echoes of Feydeau, the Spanish sainete as well as direct parodies of Zorrilla's "Don Juan." But there is much more. Its language is liberally sprinkled with anachronisms as so many capers on a succulent dish. And the G.A.L.A. production directed by Hugo Medrano misses none of the play's subtler undercurrents while maintaining an atmosphere of speedy comedy.

It is very much a sex comedy. But on the way in and out of the bedroom it manages to poke fun at most social and religious institutions. How author Martinez Ballesteros hoped to get this play past Franco's censors in 1972 remains a mystery, except that the unfailing elegance of the text goes a long way to disguise its bite.

If Noel Coward had been trained by Spanish Jesuits, the results might have sounded like this play, which is so fast and so clever that the audience often had to fight back laughter for fear of missing the next line. The performances are masterful. Hugo Medrano stars as Count Ordono, a sexy double-talking, two-timing cad who has cultivated the art of correct appearances. As his wife, Roxana, Madelain Romero projects a personality as tight as her braided bun. Antonio Salvador is all huggable innocence as the truly chaste Don Bermudo. There are many other gems in the large cast, and the brightest of all is Leonor Chaves as La Mora Moriana, the sensuous odalisque with a Cheshire cat smile. She can steal a scene with a sway of a shoulder, and her masquerade as a "Christian lady" in Act II is enough to make the evening worthwhile.

Under Medrano's sensitive direction, each character covers the stage like a lynx after small prey, and the relentlessly fast verses are always clarified in motion. Only the slide projections looked amateurish in the otherwise fine staging.

Still, the dinkiness of the slides took away little from the effect of one erotic fantasy scene in which the laughter following a particular nun joke resounded for several beats. The text is funny enough to have survived on cuteness. It received an intelligent production instead, and the result is comedy at its best.

"Romancero Secreto de un Casto Varon" plays Thursday through Sunday at G.A.L.A., 2319 18th St. NW., until May 31.