It began as a church gig, the sort of engagement young musicians take on simply to have a chance to work in their art form. But a quarter century later, it is one of the most visible performing arts bodies in New York City.

Co-founder Michael Feldman’s original duties at his job at the Greenwich Village Church of St. Luke in the Fields (it burned down in 1979) consisted of running the music program at the school. Nursing aspirations as a musical director, Feldman invited some young, up-and-coming friends to play in a chamber music series at the church. This year the St. Luke’s organization celebrates its 30th anniversary.

The orchestra’s Carnegie Hall series starts Thursday with an all-Baroque program featuring former music director Sir Roger Norrington and countertenor David Daniels. The chamber ensemble performs older repertoire at the Brooklyn Museum and Zankel Hall and new music at the Chelsea Art Museum and – starting this season – at Dia Beacon in Beacon, N.Y.

St. Luke’s is also America’s pre-eminent orchestra for hire – everything from backing up Renee Fleming in her most recent disc of arias to playing in “South Pacific.” The sheer number (up to 100) of performances a season can be aesthetically disorienting. But possibly no other performers get to play for such a wide cross section of the city’s concert-going public.

“From the very beginning, we had the idea of, ‘Let’s do a little bit of everything,’ ” said the group’s executive director, Marianne Lockwood, who has been with St. Luke’s from the beginning.

Certainly, the chamber ensemble’s first season of concerts showcased a conscious eclecticism: standards such as a “Tafelmusik” concerto by Telemann and a Mozart piano sonata, but also the obscure “Frauentanze” by Kurt Weill, fully staged performances of Haydn’s opera “Lo Speziale,” and numerous contemporary compositions.

After five years, in 1979, the group decided to add the additional layer of a chamber orchestra, with chamber being the operative word. “We used the chamber music model as the core of what we did,” Ms. Lockwood said. “Even under a conductor, the sense of who the musicians were was guided by chamber music – the sense of always listening.”

The business end of the orchestra is perhaps its most striking feature. The players have an agreement with management that allows them to work on a per-service basis. This lends the whole institution an air of flexibility and independence – and makes the Orchestra of St. Luke’s a cheaper option than hiring, say, the Philadelphia Orchestra, to accompany you.

Ms. Lockwood acknowledges the inherent dangers in such a model. “There have been jobs we’ve taken that have been questionable,” she said. “Beggars can’t be choosers, and, especially in the early days, we were beggars. In the coming years, we’d like to be more selective about our partnerships.”

But the group’s own programming has led to many fruitful and culturally significant collaborations, such as the New York premiere of John Adams’s landmark opera, “Nixon in China” in 1987 (the CD recording of which won them one of their three Grammy Awards) and performances of Faure’s Requiem that marked the United States debut of Philippe Herreweghe, one of the world’s finest choral conductors.

“We’re still trying to get him back,” Ms. Lockwood said. “The orchestra just loved him.”

Much of the new music the ensemble has championed leans toward the lighter, accessible side – Arvo Part, David del Tredici, Andre Previn – but future collaborations include a Carnegie Hall commission from a certifiably thorny composer in the 2005-6 season. (For publicity reasons, the composer can’t yet be identified.)

St. Luke’s wouldn’t be St. Luke’s, however, without the group’s educational outreach programs – it did, after all, start at a school. While such programs have become de rigueur throughout the country, St. Luke’s program was one of the first, and today it reaches a wide swath of the New York City public school system.

“In 1976, we played performances of a chamber opera for 50,000 children,” Ms. Lockwood said. “It was crazy. Now, we have developed our educational program to include school workshops, where the instrumentalists work one on one with the kids.”

Under its current music director, Donald Runnicles, the group is diversifying now more than ever. Ms. Lockwood made the interesting assertion that Thursday’s performance will be the first time the ensemble has performed an all-Baroque program. (Equally interestingly, it is the first Carnegie Hall performance of the complete score to Handel’s “Water Music” since 1963.)

While Mr. Runnicles holds sway over the orchestral repertoire, the chamber ensemble has added a new series, “Second Helpings,” which gives composers an opportunity to re-air their new works. “With the amount of effort that goes into playing new music – which requires considerably more rehearsing – it’s a shame to put all that energy into just one performance,” Ms. Lockwood said.

The addition of Dia Beacon – an acoustical puzzle, with its gargantuan, wood-floored galleries – as a new site for the “Second Helpings” series will test both the players and the audience. Ms. Lockwood, for one, isn’t concerned: “Challenges have never stopped us,” she said.

St. Luke’s in the City

OCTOBER 21, 8 P. M.

Sir Roger Norrington will conduct the Orchestra of St. Luke’s at Carnegie Hall, with guest artist David Daniels. The program includes Purcell’s “Fairy Queen Suite” and Handel’s “Arias from Ariodante, Orlando & Giulio Cesare,” and “Water Music” (881 Seventh Avenue, between 55th and 56th Streets, 212-247-7800).

OCTOBER 24, 2 P . M .

St. Luke’s Chamber Ensemble will perform an all-Bach program, including the Oboe d’amore Concerto in A major, the Harpsichord Concerto No. 5 in F minor, and the Brandenburg Concerto No. 5 in D major at the Brooklyn Museum (200 Eastern Parkway, at Washington Avenue, 212-594-6100).

OCTOBER 27, 7:30 P . M .

David Daniels will join the St. Luke’s Chamber Ensemble in a program of Bach and Scarlatti at Zankel Hall. The program will include Scarlatti cantatas “Infirmata, vulnerata” and “Perche tacete, regolati concenti?” (881 Seventh Avenue, between 55th and 56th Streets, 212-594-6100).