"Equus," which recently has been extended a month at the Source's Warehouse Rep, contains one of the roles most coveted by young actors, that of the boy Alan Strang. The boy is 17, but the emotional demands of the play are such that no one that young realistically could be expected to carry it off.

Source director Robert McNamara was fortunate to find Kryztov Lindquist for the part here. (His name is a reflection of his Hungarian-Swedish heritage.) At 27, Lindquist retains the slight frame of a younger man, yet his features have an offbeat quality that hint at Strang's darker side.

"The first agent I went to see in New York said he wouldn't sign me because I was an odd type," said Lindquist, who has played an informant and an obsessed Vietnam veteran in two small productions in New York.

Lindquist is a semi-Washingtonian, a Foreign Service brat who graduated from Frederick Douglass High School in Upper Marlboro before going on to the American Academy of Dramatic Art in New York. Since then he has lived the gypsy life of an actor, settling neither here nor there and not intending to. He appeared in three plays at the New Playwrights' Theatre in 1978, including "Hagar's Children." The part of Alan Strang has always appealed to him; he remembers reading reviews of the original British production in 1973, and later auditioned twice for the Broadway production.

"The role was always in the back of my mind. I had grown up with horses during the eight years we lived in Brazil. I started riding and eventually showing there. But I hadn't ridden for, I guess, 10 years until we started rehearsing the show."

Lindquist had a "terrible" job in a boutique before the the play opened; now he lives on a meagre stipend from the low-budget Source and "the kindness of strangers, or rather, friends." But he does not seem to be fazed by the impecunious life of a struggling thespian. "I don't know what I'd do if I didn't act," he said. "Wherever the work takes me I'll go."

In addition to horseback riding, he prepared for the role by studying "street kids."

"I didn't want to go to a mental ward," he said. "I had been in one before as a visitor. I didn't want to do a takeoff on a specific kid. Alan's psychosis, if you want to call it that, is not so dramatic. I don't see that much wrong with him for a great deal of his life. (Dr.) Dysart says in the play, "something snapped," and I think that's what happened. I don't find the worshiping of horses, or even taking off your clothes to ride them, psychotic. Bizarre, yes, but not psychotic. His crime was to destroy them, and in so doing destroy his concept of religion . . ."

He unwinds with a few drinks with the rest of the cast and then a bit of Vivaldi. His motto is a passage recalled from Jean Cocteau's "Profound Secrets," which he paraphrases: "The actor-poet doesn't prove himself by his gestures or his face or the timbre of his voice, but by an unusual quality of conduct of the soul, which stimulates the audience . . . "