New places, new faces and some new ventures promise a lively 1978-79 season for the arts in Montgomery and Prince George's counties.

The theater scene of the metropolitan area receives a significant addition on Oct. 6, when the new Round House Theater in Silver Spring opens with a production of Arthur Kopit's play, "Indians," Seating 208, the theater's intimate space provides an ideal home for Montgomery County's professional resident company, the Round House Theater Company of Street 70 Performing Arts Program.

Producing director June Allen, who has long worked for such a facility, called the theater a glorious birth after a 25-year pregnancy. For details on the seven-play season, which includes a Pinter play and Moliere's "Tartuffe," call 468-4234.

Also appearing at the theater will be its new resident dance ensemble, the Round House Dance Company. In addition, the company is establishing the Dancers' Place, an information center in Wheaton. For information on the new center call 933-7595.

An arts center for Montgomery County, another idea long aborning, has moved one step forward with the county's recent purchase of the Corby Mansion site in north Bethesda for $1,224,000. The property was designated the most desirable site for a central arts facility in a 1975 county-sponsored study.

Completion of Prince George's County's first visual arts center is scheduled for June 1979. Located on the grounds of the Montpelier Arts Center will offer county artists studio space and display areas.

Several music groups are beginning the upcoming season under new leadership. Dorothy Biondi has been named general manager for Prince George's Civic Opers, whole season opens Oct. 21 with "The Merry Widow." In addition to having been the company's stage director for five years, Biondi has been active in community and semi-professional theater in the metropolitan areas.

The Montgomery County Master-works Chorus has a new director, Edward Polochick, who also serves as assistant conductor of the Baltimore Choral Arts Society. The 26-year-old musician, a recent winner of the Stokowski Conducting Competition, will conduct the Philadelphia Orchestra next February.

Fred Morden, who has been director of Prince George's County Senior Youth Orchestra for five years, will take over leadership of Prince George's Symphony this season.

As a result of differences between symphony board members and players more than a year ago, the county still has two orchestras, the Prince George's Symphony and the Prince George's Philharmonic. Morden has stated his goal of supporting all music in the county and working in cooperation with his friend and colleague, Emerson Head, director of the Philharmonic. Head agrees with Morden's idea of exploring the possibility of unifying the two groups.

"To have two orchestras, doing the same thing, with the same goals, going after the same money, the same players and the same audience, is unfortunate," Head said.

Dr. Robert Tennyson, director of band at American University and conductor of the Rockville Concert Band, was recently appointed director of the Montgomery County Masterworks Youth Orchestra. He replaces the orchestra founder, Dr. Stephen Barnes, who has moved to Oklahoma.

Beginning its usual two Gilbert and Sullivan season in January at its usual Silver Spring location, Montgomery Blair High School, will be an old group with a new name. The Montgomery Savoyards have become the Washington Savoyards. President John Strawhorn said the change was made to reflect the group's metropolitan membership.

Two theater groups who have shared facilities in Gaithersubury will celebrate their anniversaries by merging for their season opener. Montgomery Players, marking its 50th year, and KG Players, marking its 30th, will present Preston Jones' "A Texas Trilogy" in repertory from tomorrow through Nov. 4. It will be the first Washington area presentation of the entire trilogy since its 1976 run at the Kennedy Center and the first joint venture for the two groups as well as their first time to offer plays in repertory. Mor details are available at 948-6669.

In addition to it chamber music series at the University of Maryland, University Community Concerts this season will offer Classical Vibes, a new three-concert series for children, aged 8-13, starting Sept. 16. For details on both the chamber and children's music series call 454-3322.

Feet First, a jazz dance company and school in Bethesda, has a new tap dance studio that will offer classes for all levels starting Sept. 11. Carol Vaugin, one of Feet First's directors, plans to present what she terms "a moving tap dance" in the fall. With replicans of Metrobuses attached to her tap shoes, she intends to dance here way about the Washington area aboard Metrobuses. For information on tap or jazz classes call 656-9076.

The season will find several groups in new locations. Appearing at the Publick Playhouse in Cheverly for the first time will be Prince George's Civic Opera for its December production of "Hansel and Gretel," and Prince George's Choral Society with a three-concert series. Prince George's Chamber Music Association and the Chamber Ensemble of the county Philharmonic will also make their first appearance at the Playhouse on Sept. 30, when they join with Con Viva Musica for an evening of chamber music.

This year the Playhouse will have two community theaters using the facility for their entire seasons. Joining Prince George's Little Theater, which last year presented all its plays at the Playhouse, will be the Adelphians. For more information on all events at the Playhouse call 277-1710.

The Rockville Music Theater moves to the Rockville Civic Center for its seasons, which opens in November with "My Fair Lady." The 3-year-old company placed second in this year's Ruby Griffith awards, an an area-wide community theater competition sponsored by the British Embassy Players. For detail on the company call 869-3557 or 942-4566.

Maryland Dance Theater, the rapidly growing modern dance company based at the University of Maryland, will continue to expand its touring activities this season. Included in its schedule will be the company's first tour as part of the National Endowment for the Arts dance touring program. The group will also give as first major Washington performance on Jan. 23, when it will appear at Lisner Auditorium as part of the Washington Performing Arts Society's dance series. Maryland residents will be able to see the group closer to home on Dec. 1 and 2, at the Publick Playhouse and March 9 and 10 at the University of Maryland. For more details call 454-4056.

To be congratulated on successfully staying in one place is the Plum Gallery in Kensington, where several other galleries have recently come and gone.Paula Locker, one of the owners, said that the gallery will continue to aim for the highest quality in its shows. The season opens Sept. 8 with works by New York artist Sue Fuller. For details call 933-0222.