Bartoletti, who would have turned 87 Monday, died Sunday in a hospital in Florence, organizers of the city's annual arts festival, Maggio Musicale Fiorentino, announced.
Bartoletti was 30 years old when he made his U.S. debut with the Lyric Opera in 1956. He went on to establish a reputation for his interpretation of the Italian opera repertory.
The company came to be known as "La Scala West," the Chicago Tribune said.
He served as co-artistic director with Pino Donati until 1974, when Bartoletti took over as sole artistic director and principal conductor, the newspaper said.
Bartoletti conducted almost 600 performances of 55 operas for the company from 1956 to 2007, helping the Lyric Opera Orchestra build an international reputation.
Plans calls for Bartoletti to be buried Monday in Sesto Fiorentino, the Florence suburb where he was born.
Charlize Theron not engaged to Sean Penn 'yet'
Pistorius testifies he didn't consciously pull trigger when he shot girlfriend