Kevin Wade's off-Broadway success, "Key Exchange," is a slender piece of playwriting--more than a pretext, perhaps, but something less than a text. It is the sort of piece, increasingly common in the theater, to which the actors can and must bring a lot, while the piece itself is bringing relatively little. In this particular instance, charm is probably the first thing they should bring.

Revived by Source Theatre in a new performing space at 1716 14th St. NW dubbed the Resource, the 90-minute, intermissionless play is made up of the passing encounters of Michael, Philip and Lisa--bicyclists three--on consecutive summer weekends in Central Park. Michael (Bill Wkering with their racing machines. Too cool for big emotions, too confused for articulate thoughts, they are trying to sort out their place in the great sexual revolution. The notion of commitment hangs in the summer air, but it is approached only tangentially or with a tinge of embarrassment.

Michael's wife will eventually come back to him, and Lisa will turn the tables on Philip, but nothing wildly dramatic is in the cards. What the play has to offer, if the actors are right, is a casual, understated climate, the mood of which is vaguely sweet, vaguely sour. Action is reduced to the offhanded, sometimes well-intentioned fumblings of young people indirectly tackling such sticklers as Love and Devotion.

At the Resource, director Brian Nelson has a tendency to treat the play as if it contains great verities, instead of recognizing it as a piece in need of beefing up. Still, the work on display is honest and the acting is proficient. However, only one cast member, Bill Whitaker, has the easy appeal and personality to fill in the play's blanks. Looking a little like the kid brother who grew up, possessed of a goofy grin that just can't stay off his face for too long a time, he radiates a most congenial presence. Who wouldn't stop in the park and shoot the breeze with him?

Sitler and Magathan have to work harder at being appealing, especially since their relationship is going through a sticky period and they are stuck with lines along the order of "What are you so scared of? You either want me or you don't." Unfortunately, the two performers don't necessarily constitute one of those natural biological pairs you instinctively root for. In this case, that's a serious shortcoming. Whitaker ends up pretty much pedaling this vehicle on his own.

As for the Resource itself, it is for the time being less a theater than a store emptied of its merchandise. Chairs have been assembled along the walls, with a narrow acting area extending down the middle of the room. The unvarnished arrangement is not especially propitious for drama, and spectators can be forgiven, as their heads swivel back and forth, if they have the momentary sensation of watching a tennis match.