NEW YORK — Carl Drews still remembers the first time he heard the "Hallelujah" chorus. His parents had taken him to see "The Greatest Story Ever Told," the movie about the life of Jesus with a soundtrack including the famous chorus from Handel's "Messiah." It made the little boy feel that heaven was a place "where you sing the 'Hallelujah' chorus forever and ever."

Years later, on a Habit for Humanity project in Nicaragua, the longtime choir singer sang the stirring words from memory under the newly built roof of a house, banana trees swaying in the breeze, with two other volunteers on his work crew.

This December, Drews, a 49-year-old software engineer, will participate in the 27th annual "Messiah" sing-along in Boulder, Colo., one of hundreds of such events across the country in which an unrehearsed audience performs as the chorus in George Frideric Handel's baroque masterpiece.

"It's just really fun to be with people singing their hearts out," Drews said a few weeks after rehearsals began in Boulder for the core group of singers who support the audience. "And I am a Christian so I am singing what I believe."

But you don't have to be a Christian to love "Messiah." Tens of thousands of Americans from all different social and religious backgrounds will gather in churches, concert halls and living rooms beginning in mid-December to sing all or parts of the two-hour oratorio.

Many will have had some musical training, but others will barely be able to carry a tune.

In Chicago, some 7,000 people are expected at two performances of the Bank of America Do-It-Yourself Messiah, which will be performed at the Harris Theater for Music and Dance in Millennium Park. As many as 3,000 people will pile into New York's Avery Fisher Hall when the National Chorale hosts its 42nd Messiah Sing-In. About 200 people will show up for each of three concerts in Boulder, and thousands more will participate in similar events at points in between.

The origin of the sing-along is a little murky. Similar unrehearsed performances where the audience serves as chorus occur in Great Britain, where they are known as "scratch Messiahs," as in cooking from scratch. Graydon Beeks, a music history professor at Pomona College and president of The American Handel Society, says sing-along Messiahs seemed to catch on big here in the late 1960s and early '70s. He remembers going to one such event with about 50 people when he was a college student in the late '60s — but that was in the home of a family friend who was a professional pianist.