Street 70, Montgomery County's novel band of performers-teachers, is reading a production of "Godspell" to open its unusual new theater, The Round House, 12210 Bushey Dr., Wheaton. It will play March 10 through April 3.

The name stems from an experimental elementary school of round design that was phased out of the county's school system two years ago.June Allen, of the county's department of recreation, saw the building as a home for the teaching and performing group she has been developing since 1970.

Ever so gradually, Street 70 has made itself felt within Montgomery's borders. Its dozen members have appeared through the years in Montgomery schools.

When the notion of turning the unused school into headquarters for the recreation department was born, 100,000 persons signed petitions favoring the project. A group called "Friends of Street 70" had hit the suburban street for support.

While renovations are net wholly complete, a "slice of the round school pie," once the school's gym, will be ready enough for "Godspell" next week. Allen, technical director Ben Hooks and the performers have been doing their own work. After the "Godspell" run, The Round House will be closed for completion by next fall, when a series of regular performances will be inaugurated.

While no one is vowing that a county theater may not exist elsewhere, Street 70 seems to be a unique institution. States and cities have their official theaters. But is there another county supporting one?

The teachers-performers, or performing teachers, are salaried employees of the county and have worked closely together for four years. All agree that such closeness has been stimulating. "Four years ago," said one of the "Godspell" cast, "we couldn't have attempted this musical."

Roger Ames, music director of West-moreland Congregational Church, is music director. Other regulars include Irene Crist, Gayler Behrman, Cathy Graham, Betty Clark, Eliot Pfanstiehl, Michael Littman, Will Robertson, Jeff Davis and Jerry Whitton, who will play Judas. Jesus will be performed by a longtime member of the group. Michael Hume, who recently appeared with the Folger Theater Group and is in professional demand the part of the Celebrant in Bernstein's "Mass," an assignment he succeeded to in the original company.

Tickets for the nightly performances at The Round House will be $3.50 until March 9 and $4.50 thereafter. Group and advance reservations may be made at 468-4172.