LOS ANGELES, May 8— Neil Bogart, the entertainment executive whose discoveries ranged from Donna Summer, the disco singer, to Curtis Mayfield, the composer of ''Shaft,'' died of cancer today at Cedars-Sinai Medical Center. He was 39 years old.

Casablanca Records and Filmworks, both founded by Mr. Bogart, made millions of dollars from such movies as ''Midnight Express,'' ''The Deep'' and ''Thank God It's Friday'' and struck gold in the late 1970's with a string of disco recordings by Miss Summer, the Village People and others.

Mr. Bogart and his partners sold their controlling interest in Casablanca to the German-based Polygram Group two years ago, but Mr. Bogart turned around and founded Boardwalk Entertainment, which has also produced hit records.

A native of Brooklyn who sepnt 20 years in the entertainment business, Mr. Bogart started his career as a singer but quickly turned to behind-the-scenes work. By the age of 25, he was general manager at Cameo-Parkway Records and was known in the industry as ''The Kid.'' Dubbed 'The Bubblegum King'

In a later executive position at Buddha Records, he helped build the successes of Mr. Mayfield, who wrote the award-winning score for the movie ''Shaft.'' Hits by other Buddha acts such as Melanie, the Isley Brothers, the Edwin Hawkins Singers and Peter Noone, who was better known as Herman of Herman's Hermits, caused Time magazine to dub Mr. Bogart ''the bubblegum king,'' from the common term for that type of popular music.

In 1973, Mr. Bogart fulfilled a longtime dream by founding his own record company, Casablanca. The company's first major success was taking on the then unknown singer-producer team of Miss Summer and Giorgio Moroder. They put together a 17-minute number called ''Love to Love You, Baby'' that became one of the first giant disco hits. Mr. Bogart soon had another nickname: ''the disco king.''

Casablanca expanded into films marked by successful soundtracks: Academy Awards were given to Mr. Moroder for his ''Midnight Express'' score and to Paul Jabara for the theme for ''Thank God It's Friday,'' which was called ''Last Dance.''

Casablanca's heyday ended with the demise of disco, but Mr. Bogart was quickly successful with Boardwalk, whose artists included Harry Chapin, the late singer-composer; Mac Davis, and Ringo Starr. Served on Several Boards

Mr. Bogart was also active in community affairs, serving on the board of governors of Cedars-Sinai Medical Center. He was executive vice president of the Betty Ford Cancer Society and served as a commissioner of the California Museum of Science and Industry and of the Los Angeles Memorial Coliseum. He was co-chairman of the Los Angeles Music Center's entertainment committee.

Mr. Bogart is survived by his wife, Joyce, and four children; his parents, Ruth and Al Bogart of Encino; a sister, Bonnie Ermillio of Los Angeles, and two brothers, Lance Bogart of Hollywood and Ira Bogart of New York City.

A memorial service is scheduled for Tuesday at Hillside Chapel in Los Angeles.