Montgomery County's Street 70 Performing Arts Program now is in residence at Round House Theater. Very few other American counties - if any - support such a facility.

Arthur Kopit's "Indians" is the official opening attraction at the 208-seat theater at 12210 Bushey Dr. (Veirs Mill and Randolph roads) in Silver Spring.

With its semi-thrust stage, the theater is a small, handsome gem of pleasing reds, browns and sightlines. Decreasing enrollment caused the closing of Bushey Drive Elementary School, and producing director June Allen immediately saw that, with the right alterations, the space could be used for the group which had its informal start 25 years ago and which has been operated by the county since 1973.

Architect Michelle Honey's transformation of the school for office, theater and elderly day-care facilaities nicely disguises built-in limitations. Adjacent parking space is well lighted and the lobby is a pleasing introducing.

Under artistic director Jeffrey B. Davis, Street 70 performs in schools, playgrounds and churches, and its staff teaches dance, mime and acting to children of several age groups.

With the performer-teachers salaried by the county, the boast is made that Round House is "the area's newest professional theater." That does shade the truth a trifle, for these are not Equity players, the accepted norm for "professionals"; but they are, after all, earning their livings at their craft.

"Indians" shows the company's standards to be modest but, in major roles, there is solid competence. Evidently a veteran of the troupe, Jerry Whiddon is a confident Buffalo Bill and Gary Phillips proves to be an able character actor as Wild Bill Hickok. On cannot cavil but one can't swoon with discovery, either.

Performances are Wednesday through Sunday evenings at 8 through this month.

Seven adult productions are planned for this first Round House season, to include "The Caretaker," "Tartuffe," "The Owl and the Pussycat," "Mime Concerto" and "Man of La Mancha."

Smaller works will be done in a "Meet the Artist" series: "The Belle of Amherst," "Abelard and Heloise" and "The Public Eye" and "The Private Ear." There also will be a Saturday afternoon series addressed to grade-school children. Further details at the box office, 468-4234, between 1 and 5 p.m. daily.