Ira Gershwin, 86, who set words to the music of his brother, George, and other composers and thereby produced some of the best-loved songs in the world, including "The Man I Love," "Fascinating Rhythm" and "Summertime," died yesterday at his home in Beverly Hills, Calif. The cause of death was not reported.

Mr. Gershwin, a shy, witty and literate man who looked like Central Casting's idea of a college professor, had an unerring instinct for lyrics that were singable as well as memorable. This won him a major place in 20th century American music. Among his contemporaries, only Cole Porter and Irving Berlin were his peers, according to many critics.

The first published collaboration of the Gershwin brothers was "Waiting for the Sun to Come Out," part of "Sweetheart Shop," a musical that appeared in 1920. They went on to collaborate on about 18 musicals, including "Funny Face" (1927), "Of Thee I Sing" (1931), and the opera "Porgy and Bess," which opened on Broadway on Oct. 10, 1935, and has since become a classic.

The brothers Gershwin also wrote the words and music for several films and these included "Shall We Dance?" (1936) and "A Damsel in Distress" (1937), both of which starred Fred Astaire. On July 11, 1937, before "Damsel" was finished, George Gershwin died.

Although George Gershwin, composer of "Rhapsody in Blue" and "An American in Paris," is the better known of the two, Ira Gershwin received numerous honors. In 1931, he shared a Pulitzer Prize with George S. Kaufman and Morris Ryskind for "Of Thee I Sing," the first musical to win that prize in the drama category.

But more to the point, the work Ira Gershwin did with his brother and other composers still is remembered, sung and performed, and has become part of the country's heritage.

On May 1, the musical, "My One and Only," made up of songs by the Gershwins with a new book by Peter Stone, opened on Broadway with Twiggy and Tommy Tune. It is one of the hits of the season.

The theater at which it is playing, formerly the Uris, is now called the Gershwin.

"Ira was thrilled with the success of 'My One and Only,' " Stone said yesterday. "I'm very happy that he lived to see this last success because it's a Gershwin success--the stars of the evening are really George and Ira Gershwin."

Alexander H. Cohen, the producer of the Tony Awards broadcast on television on June 5, said the program paid tribute to the brothers because "that is how the American musical community felt about George and Ira Gershwin."

In the course of his career, Ira Gershwin collaborated with a number of composers besides his brother. He wrote lyrics for tunes by Harold Arlen, Vernon Duke, Vincent Youmans, Jerome Kern, Kurt Weill, Sigmund Romberg, Harry Warren, Arthur Schwartz, Burton Lane and E.Y. (Yip) Harburg.

"Girl Crazy," which he wrote with his brother in 1930, brought Ethel Merman to Broadway. "Lady in the Dark," on which he collaborated with Weill in 1940, made a star of Danny Kaye. With Arlen, he wrote the songs for "A Star is Born" (1954) in which Judy Garland sang "The Man Who Got Away."

On "Porgy and Bess," Ira worked closely with Du Bose Heyward, the author of the novel "Porgy." The opera is about poor blacks living along "Catfish Row" in Charleston, S.C. Its songs include "Summertime," "It Ain't Necessarily So" and "I Got Plenty of Nuthin.' "

Other Gershwin favorites are "Embraceable You," "Strike Up the Band," "Let's Take a Walk Around the Block," "Who Cares?" "I Can't Get Started With You," "Love Walked In," "My Ship," " 'S Wonderful, 'S Marvelous" and "Jenny."

When asked which of his songs he liked best, Mr. Gershwin said, "The favorite answer of some writers is 'the latest one.' But, generally, a more truthful answer is 'most of them.' " He also was asked which came first, the music or the words. Mr. Gershwin said he normally fitted his words to music. But he added, "What usually comes first is the contract."

Regardless of what came first, Mr. Gershwin kept in mind the fact that songs are to be sung, and some sounds are easier to sing than others. Richard Coe, the drama critic emeritus of The Washington Post, has written that Mr. Gershwin avoided ending his lines with d, t, b, k or f sounds, which are hard to sing. An example cited by Coe are the lyrics to the hit "Do, Do, Do," part of "Oh, Kay!," a 1926 musical.

Ira Gershwin was born on Dec. 6, 1896, in New York City, the eldest of the four children of Morris and Rose Gershwin, who had emigrated from Russia. His father had a number of small businesses.

Ira was a bookish youth. At the City College of New York, he contributed to student journals, and later spent a year in a premedical course at Columbia University. But it became clear to him that he wanted to write, and he received $1 for a story he sent to the magazine Smart Set, which was edited by H.L. Mencken and George Jean Nathan. Ira also worked for his father and a traveling circus and was a shipping clerk and a drama critic.

By 1918, George Gershwin was beginning to make his name as a composer. Ira decided to try his hand as a lyricist. At first, he used the name Arthur Francis (taken from the names of his brothers and sister) so he could maintain an identity separate from that of his brother. He used the pseudonym for "A Dangerous Maid," an unsuccessful musical he wrote with George in 1921.

Ira Gershwin's first big success was "Two Little Girls in Blue," for which Vincent Youmans and Paul Lannin wrote the music. The show was produced in 1921 and ran for a year on Broadway.

After his brother's death, Mr. Gershwin spent much of his time in Hollywood. He enjoyed the race track and the poker table and the company of friends. He had been in failing health since the mid-1970s.

Survivors include his wife, the former Leonore Strunsky, of Beverly Hills, and a sister, Frances Godowsky of New York City.