Though perhaps best known for scoring non-musical plays, Mel Marvin is in the throes of composing two new musicals, one, headed towards Broadway (Elmer Gantry, to be directed by James Lapine), another opening Off-Broadway Feb. 7. The Portable Pioneer And Prairie Show, with a book and lyrics by Marvin and David Chambers, is being produced by the Melting Pot Theatre Company at the Theatre of the Riverside Church, through Feb. 23.

The show, developed in the 1970s on a commission by MN's Guthrie Theatre, tells of the Andersson family who, fleeing a bad harvest, leave Sweden for Minnesota in the mid-1800s. Through song and dance, Karin and Paul Andersson take their "traveling wagon show" on the open road.

Marvin was nominated for a Tony for his work as co-conceiver on the revue Tintypes, and he scored the Broadway plays Yentl and A History Of The American Film. Not only is Marvin working on a Gershwin revue with Mark Lamos (Gershwin's Fascinatin' Rhythm; he's written the music for Tony Kushner's latest, Hydriotaphia, due for a workshop at NYU's Tisch Graduate Acting Program in Spring 1997. Marvin's work has also been heard Off-Broadway at Lincoln Center, the American Place, Manhattan Theatre Club and the Chelsea Theatre Company.

Chambers, director of Christopher Durang's aforementioned American Film, as well as Howard Korder's Search And Destroy, is an associate artist at South Coast Rep.

Lori Steinberg, a protegee of Jerry Zaks, directs The Portable Pioneer And Prairie Show. Appearing in the wagon will be Larry Cahn, Samuel D. Cohen, Susan Emerson, David Lutken, Sean McCourt, Rebecca Rich and Leenya Rideout. Melting Pot, a new company, hopes to present 3-4 shows each year that "reflect the cultural diversity of NYC and the Upper West Side."

For tickets ($25) and information on The Portable Pioneer And Prairee Show, which began previews Feb. 5 at the Theatre of the Riverside Church on 120th St., call (212) 279-4200.

--By David Lefkowitz