Imagine the hero -- a dashing Russian nobleman who wants to expand Russian-American trade and "bring the two countries closer together."

Sailing across the Pacific, he reaches San Francisco and falls in love with the daughter of the governor of what was then a Spanish colony. They make love on stage amid deafening percussion, clouds of dry-ice smoke and a red and blue laser pulsing through the theater, and they vow to spend the rest of their lives together.

But there is a hitch. The heroine is Roman Catholic, and the hero, who is Russian Orthodox, feels the duty to seek official sanction from Moscow. He travels by horse across Siberia, falls ill on the way and dies. With him dies the attempt to bring America and Russia closer together.

This is the first full-scale rock opera staged here, and there is a moral to the tale: Yes, the adventure failed, concedes the narrator, "but we have to thank [the hero] for trying." The author of the lyrics, poet Andrei Voznesensky, drops some heavy clues along the way to set this "Romeo and Juliet" variation against a clear parallel of Soviet-American relations.

A few lines could have come straight from the official Soviet news agency, Tass. The hero is concerned about "increased international tensions." He sings of peace, love, understanding and "cooperation" between the two countries.

Wednesday's premiere of "Juno and Perchance " has sent the Moscow arts world buzzing and seems certain to become the sensation of the fall season, when its run begins -- unless censors get second thoughts.

The chic, young Soviets who attended the opening responded with enthusiasm to bold departures from the otherwise prudish citadel of Soviet culture. Apart from the simulated sex scene, the actors used a profane expression to describe the sexual act. The hero loudly mused that "there is no freedom" in either Russia or America. The failure of his mission to improve relations between the two countries was not ascribed to American perfidy or scheming. Rather, it was left in the marky realm of happenstance.

The two-act rock tragedy is based on the true story of Count Nikolai Rizanov, who led a Russian naval expedition to San Francisco in 1806. And at the onset of detente in 1972, Voznesensky used this story as the basis for a long, politically oriented poem, published in the United States in 1974 under the title "Story Under Full Sail."

The superb cast, directed by Mark Zakharov, one of this city's most adventurous directors, was aided by spectacular choreography by Vladimir Vasilyev, a top Bolshoi Ballet dancer.

The opera borrows from the 1960s Western youth revolt. It mingles rock harmony and dissonance. The musicians are dressed almost like Hell's Angels and the ritual chants are reminiscent of "Jesus Christ Superstar" -- all carried out against a background of symbols of the Russian Orthodox Church.