Participants in Salt Lake City's 11th annual Messiah Sing-In jam Symphony Hall to the rafters Sunday night to welcome the Christmas season with song. Many would-be songsters had to be turned away from the event, which was sponsored by the Deseret News and Utah Symphony Chorus. Free tickets disappeared within a couple of hours of becoming available. Singers responded with a fair degree of accuracy as conductor Ed Thompson tackled some of the more florid and less familiar choruses, and the huge choir of 2,700 clapped loudly for itself and soloists Noemi Lugo, Julie Reynolds, Terrance McCombs and Steven Meredith. The Sing-In's popularity may prompt sponsors to make it a two-night event next year.