Joan Diener, whose lush beauty, showstopping stage presence and operatic voice made her a favorite in musicals, especially in the original 1965 "Man of La Mancha" as well as its revivals as late as 1992, died on Saturday in Manhattan. She was 76.

The cause was complications from cancer, her daughter, Jennifer Marre, said.

Ms. Diener was best known for her role as Dulcinea in "La Mancha," a musical version of "Don Quixote" by Cervantes, with music by Mitch Leigh and lyrics by Joe Darion.

Ms. Diener, a blonde, played the brunette country wench Aldonza, who becomes the princess Dulcinea in the fevered imaginings of Cervantes's knight errant. (Sophia Lorenplayed the role in the 1972 film version.)

Ms. Diener said she was grateful for the work because it was a showcase for her vocal range and saved her from being typecast as a blonde.

In 1965, when she was 35 and starring in "La Mancha," Ms. Diener told an interviewer that when she was first noticed as a young actress, the only offers she received were for "the Jayne Mansfield-type part."

"And really that's so foreign to me," she said. "I don't do it well. If I'd had to work, I'd have taken them. But since I was married and wanted a family, I could afford to wait."

Born in Columbus, Ohio, on Feb. 24, 1930, Ms. Diener attended Sarah Lawrence College in Bronxville, N.Y., where she majored in psychology and moonlighted as a stage actress.

A Life magazine photographer noticed her in a bit part in the 1950 comedy "Season in the Sun" and she was prominently featured in the magazine. The publicity led to more parts and eventually to a featured role in "Kismet," the 1953 musical set in old Baghdad. "As an abandoned hussy, brazenly made up and loosely clad, Joan Diener looks like a fine case of grand arson," Brook Atkinson wrote in The New York Times.

But the production was troubled; Ms. Diener left a London production in 1955 under disputed circumstances. In 1965, after a 12-year absence on Broadway, she opened in "Man of La Mancha," directed by her husband, Albert Marre, who had also directed "Kismet."

"La Mancha" began at the ANTA Washington Square Theater and then moved to Broadway. "Joan Diener's performance is a puzzle," John S. Wilson wrote in The Times in his review of the original cast recording. "She has plenty of voice when she chooses to open up in operatic style. Most of the time, however, she uses a rather flat, colorless manner of singing. "

Still, Ms. Diener remained a favorite of audiences and producers, starring in "La Mancha" revivals in Los Angeles and New York. In the last weeks of a 1992 Broadway production, she succeeded Sheena Easton, the pop singer, who had left the show.

In addition to Ms. Marre and three grandsons, all of Brooklyn, Ms. Diener is survived by her husband and a son, Adam Marre, both of Manhattan.