Along with the sing-along, instructions are given, at Ford's Theater, for a cheer-and- hiss-along, to accompany the new melodrama "The Orphan's Revenge."

The times being what they are, it is necessary to explain that the cheers should be for the beautiful, selfless heroine and the brave hero. "Moving right along to vice . . ." continues the audience-reaction instructor, who later appears as the villain -- whereupon a member of the opening-night audience shouted "Yay!" and the villain, with a dignified "You anticipate me, sir," had to explain that vice is supposed to be hissed.

The fact is that audience participation is a lot of fun, and this show, with its Goldilocks heroine sacrificing herself to keep the orphanage from being recycled into a saloon, is just appealingly silly enough to inspire it. The impulse to shout "Don't do it!" when the hero is tempted to gamble away his entire $50 fortune is resisted only by the shyest.

Such an experience should come as a revelation to children who have known only the extremes of talking back to television sets and sitting in hushed reverence in theaters. This show not only encourages response, but the actors, in turn, respond to some of the shouted advice. One wouldn't want this at every play, but it's a vivid example of what the liveness of live theater means, and a child who experiences it is unlikely to remain quite as satisfied afterward with pre-recorded performances.

Gene Casey, Suzanne Buhrer and Jan Casey wrote the show, which is subtitled "Abandoned at Coopers Crossing," and Buhrer is peppy as an embittered saloon- keeper with a heart of gold. Most of the cast is merely adequate to the stock characters, but Lindy Nisbet, as the heroine, adds some fresh charm, and Roxann Parker contributes some of the sillier expressions to the role of a wicked woman.

ORPHANS' REVENGE -- At Ford's Theater through March 28.