A piece of scenery fell on to the stage at the Kennedy Center Opera House last night, fracturing the shoulder of famed ballerina Natalia Makarova and shutting down a performance of "On Your Toes."

Makarova, a former star of the Kirov ballet who defected from the Soviet Union in 1970, was taken to George Washington University Hospital, where she was treated for the fracture and a laceration of the head, which required six stitches. The injuries were expected to force her to leave the Washington run of the show.

The 42-year-old performer was near stage right in the second act of the musical revival, when, according to witnesses, a metal pipe used to weight a backdrop plunged from high above, grazed her head and struck her right shoulder.

Before a stunned audience estimated at 1,800, Makarova fell to the floor. Over the body microphone she wore, according to witnesses, came the sound of moaning.

For a moment nobody seemed to move, witnesses said. Then other performers ran to Makarova's aid, and began struggling with the pipe that had come to rest across her body.

In a few more moments, the main curtain was brought down. From behind the curtain, over the microphone Makarova still wore, according to one spectator, came groans of "My arm, my arm."

While sounds of movement continued behind the curtain, the audience in the 2,200-seat Opera House, seemed to remain transfixed, said Renee Chilton of Silver Spring.

Finally, she said, a man came from behind the curtain to announce that the show, a revival of a 1936 Rodgers and Hart Broadway show, would not continue.

He gave no explanation. A few members of the audience shouted, "How is she?" but there was no response. The man returned behind the curtain, and the audience began to leave.

"From the point of view of the Kennedy Center, it's terrific news that she escaped serious injury," Tom Kendrick, the center's operations director said early today. "Nevertheless, she's got a fractured shoulder blade and that's very serious for a dancer. . . . It obviously means she won't be able to dance until her scheduled replacement Jan. 4 , he said.

A fire department ambulance was called to the center at 10:22 p.m. and took Makarova to the hospital. A paramedic who rode with her said the ballerina was conscious and "was talking to us."

It was not immediately clear early today whether she would be admitted to the hospital, where she arrived with a blond wig glued and taped to her head.

Meanwhile, authorities said that the show's two performances today would go on as scheduled, with an understudy filling in for Makarova.

The revival, directed by George Abbott, opened here Dec. 14, and Valentina Kozlova was scheduled to replace Makarova on Jan. 4 in the role of a temperamental Russian ballerina.

Kennedy Center authorities said last night that it was possible that Kozlova might now be brought in sooner.

Last night's incident occurred in the second act near the end of the show. The piece of scenery involved was described as a backdrop that depicted the back of the outside of the "Cosmopolitan Opera House." The metal pipe, described by a Kennedy Center spokewoman as about one inch in diameter, was attached at its bottom to keep it taut.

When not in use, the backdrop hung in the flies, above and behind the proscenium. After the fourth scene, the drop was being raised in preparation for the fifth, authorities said, when it appeared to tear. The part attached to the pipe ripped away from the upper part of the drop.

Witnesses in the audience said that the pipe fell to the stage with a resounding crash, and may have bounced before striking the ballerina.

"It was unbelievable," said Barbara Plummer of Wheaton, who was in the audience. "It could have hit many people."

When Makarova defected in September 1970, her reasons were listed as the reactionary state of the dance in the Soviet Union and an unwillingness there to experiment.

As a performer with the celebrated Kirov Ballet, she danced in Washington in 1961 and 1964 in the classical roles for which she had won international renown.

The ballerina who last night performed in a Broadway musical comedy had won special acclaim for her performances in such ballet classics as "Giselle" and "Swan Lake," in which she danced the role of Odette.

As a dancer in classical ballet she has won admiration for projecting a delicate perfection.

Off stage, those who met her after her defection found her sprightly, fun-loving and impetuous.

In the years after her defection she continued to reign as an international superstar, expanding her horizons to include ballets by such contemporaries as Jerome Robbins, Antony Tudor and George Balanchine.

Balanchine choreographed the original and present production of "On Your Toes."

The show includes such perennial musical favorites as Richard Rodgers' gently melodic "There's a Small Hotel." It is also remembered for the ballet "Slaughter on 10th Avenue."

That ballet and Balanchine's "Princess Zenobia Ballet" have been credited with the original success of the show, which chronicles the fortunes of a Russian ballet troupe in New York.

After the announcement that the performance would not continue, patrons said ushers said ticket stubs should be retained. No plans for any adjustment of tickets could be learned last night.

Prior to the accident, Chilton said, "the performance was quite good. "We were enjoying it," she said. "We were looking forward to the remainder of the show."