Stephen Simon, a conductor who became a leading specialist in the compositions of George Frideric Handel and who founded musical ensembles in Washington and New York, died Jan. 20 at a hospital in New York City after a stroke. He was 75.

A family assistant, Lee Ryder, confirmed the death.

Mr. Simon built a reputation as a Handel expert in the 1960s when he conducted some of the first recordings of many of the 18th-century composer’s operas and oratorios.

He was music director of the Handel Festival in New York from 1971 to 1974, and his recording of Handel’s oratorio “Solomon” with the Vienna Volksoper Orchestra earned a Grammy Award nomination in 1969 for best choral recording.

“The idea that one would have all of the operas and oratorios recorded was something that we really couldn’t have imagined at the time,” said Donald Burrows, a Handel scholar and music professor at the Open University in England. “These were three-hour works. At a certain stage, he was in the pioneering bracket of just getting performers together to do such large work.”

“Solomon” was a demanding piece to record because it required a double choir, Burrows said.

Mr. Simon settled in the Washington area to start the Handel Festival Orchestra in 1976. The orchestra, later known as the Washington Chamber Symphony, performed at the Kennedy Center and was a pivotal force in the revival of Handel’s lesser-known works.

Partly through the Kennedy Center’s annual Handel Festival, Mr. Simon was credited with exposing audiences to vast amounts of Handel’s repertoire beyond the “Hallelujah” chorus from his “Messiah.”

“Handel — everything you do of his becomes a continual learning process,” he told the New York Times in 1972. “There is a lift in his style that is wonderful.”

Music critics noted Mr. Simon’s ambitious endeavor to animate Handel’s music in non-traditional ways, emphasizing multiple soloists and the personality the soloists brought to the Baroque tradition.

“It’s such irresistible music — blast those trumpets; build that fugue; call out those massed voices; stop on a dime for a grand Handelian pause, the world ringing in your ears — and Simon makes it all seem like so much fun,” music critic Tim Page wrote in The Washington Post of a 1996 concert that included the “Hallelujah” chorus and lesser-known Handel works such as “Semele,” “Samson,” “Saul,” “Solomon” and “Judas Maccabaeus.”

Mr. Simon was an heir to the Annenberg fortune. He and his wife, Bonnie, often used their own money to keep the Washington Chamber Symphony afloat.

The organization disbanded in 2002 because of major financial difficulties.

Mr. Simon also cited the plummeting support for arts funding after the Sept. 11, 2001, terrorist attacks.

“Unfortunately, in the past year, changes in our world affected the orchestra to the same degree as it did other businesses,” Mr. Simon said at the time in a letter to subscribers. The Post reported that subscribers were not reimbursed until two years after the symphony disbanded and, to much outcry, they received a fraction of what they had originally paid.

Stephen Anthony Simon was born May 5, 1937, in New York City. His maternal grandfather was the publisher Moses Annenberg, and his uncle was Walter H. Annenberg, the publisher, philanthropist and former ambassador to Britain.

Mr. Simon graduated from Yale University with a bachelor’s degree in music in 1960. He studied with Austrian conductor Josef Krips.

Mr. Simon and wife Bonnie moved back to New York City from the District in 2009. After the WCS folded, he founded the Simon Sinfonietta and L’Orchestre des Portes Rouges.

In 2004 Stephen and Bonnie Simon co-founded Maestro Classics, a line of classical music CDs for children. He ran multiple music programs for children during his career.

His first marriage, to Ellen Friendly, ended in divorce. Survivors include Bonnie Ward Simon of Manhattan, his wife of 35 years; four sons from his first marriage, Daniel Simon and James Simon, both of Manhattan, David Simon of Brookline, Mass., and Adam Simon of Concord, Mass.; two sons from his second marriage, Basil Simon of Boston and Sebastian Simon of Manhattan; and four grandchildren.

Mr. Simon was a jazz enthusiast in college. He said he found a same exhilarating improvisational quality to classical music.

“There is a close link between jazz and Baroque music because of improvisation,” he told the Times in 1972. “Knowing the style makes you feel secure and then you can do anything — even if it doesn’t always work — and that’s exciting.”