Gregory Mitchell, the actor who suffered a heart attack Nov. 11 during a performance at the Kennedy Center, died yesterday at Washington Hospital Center.

Luis Perez, a dancer and choreographer who had known Mitchell for nearly 30 years, called him a "true theater warrior."

Mitchell was an intense, reliable actor and dancer who appeared in 15 New York plays, including two revivals of "Man of La Mancha," a revival of "Chicago" and the original "Kiss of the Spider Woman." He had also appeared in popular daytime soap operas and in television commercials.

Mitchell, 52, collapsed while onstage with Mikhail Baryshnikov in the drama "Forbidden Christmas, or the Doctor and the Patient" during the second of its six-performance run. After a doctor in the audience attended to him, Mitchell was taken to George Washington University Hospital and later transferred to Washington Hospital Center.

"We are devastated by this," said Christina Sterner, the managing director of the Baryshnikov Dance Foundation. Mitchell had joined the company six weeks ago. His friend Perez, the show's choreographer, replaced Mitchell and finished the short run at the Kennedy Center. The company then canceled the remainder of its tour.

"He was very straightforward, open, willing, and he was very earnest," Baryshnikov said yesterday. "He had a very clear understanding of what his task was in the play." The play by Rezo Gabriadze about a doctor and his patient, who thinks he is a car, was the first time Mitchell and Baryshnikov had worked together. "I remembered him from his early days with the Eliot Feld company," Baryshnikov said. "He had a bright and lively personality, very outgoing. Then I saw him occasionally on Broadway and in commercials."

Chita Rivera, the Tony Award-winning singer and dancer whose career stretches back to "West Side Story," said she rated Mitchell among the great Broadway dancers. She recalled a scene from "Merlin" in which she played the queen and Mitchell the queen's companion. "I would look to my right, and he would take five or six steps from the wing. And when he hit the stage, he was in a full arabesque. He was one of the most powerful dancers, and he really challenged me," Rivera said. "Plus I could not keep my eyes off him." They had recently done a workshop production based on her life. "He played each of the men in my life, and I have never danced with a guy like this. He is really a guy-guy."

Mitchell, a graduate of Juilliard, was born in Brooklyn, N.Y., and listed on his resume that his accents included Italian, Spanish and Brooklyn. His other Broadway shows included "Steel Pier," "Victor/Victoria," "The Phantom of the Opera" and "Kicks." He appeared in the award-winning film version of "Chicago," as well as in "Random Hearts," "Cradle Will Rock" and "A Chorus Line."

In "Forbidden Christmas," Mitchell played an angel. He was performing a scene in which the angel is trying to rescue the Baryshnikov character, a retired sailor who has thrown himself into the sea. Suddenly, Mitchell fell backward, his wings making a crunching sound as he fell, according to a member of the audience.

"I thought he had tripped. I thought it was a joke. I couldn't believe that it would happen that way," said Baryshnikov, who said the dancer never regained consciousness.

Mitchell's friends remembered a snappy dresser who was intensely proud of his two sons, Garrett, 16, and Chase, 10. "He lived life to its fullest," Perez said. "He also had the longest stride of any man I have ever seen. He adored life, and he adored everything about it."

A memorial service will be held in New York soon, Perez said.

Gregory Mitchell, 52, suffered a heart attack Nov. 11 at the Kennedy Center.