When the Manhattan String Quartet opens the eighth season of the Dumbarton Concert Series Saturday at Dumbarton United Methodist Church in Georgetown, it will be a kind of bon voyage performance. The quartet, based in New York City, will be playing its last concert before leaving Nov. 2 for a 10-day tour of the Soviet Union.

At the invitation of Ambassador Arthur Hartman, the group is expected to perform at the U.S. Embassy in Moscow, the Moscow Music Conservatory, the Composers' Union and the American consul's residence in Leningrad. During the tour, the quartet -- fulfilling its role as a cultural emissary -- will play works by Shostakovich; an arrangement of Jerome Kern's "Smoke Gets in Your Eyes"; the group's signature piece, Puccini's "Chrysanthemum"; and a piece for string quartet by John Lennon, a University of Tennessee music professor who will accompany the group on the tour.

Call 965-2000 for information about the Dumbarton Concert Series. Celebrating India

Festivities celebrating the culture and customs of India -- "The Festival of India" -- continue through Saturday . . . in Frostburg, Md. Yes, Frostburg State College and a few other institutions in the Allegany County town about 80 miles northwest of Washington are holding their own Festival of India, which began Sunday.

The program differs slightly from the exhibits, performances and demonstrations of Indian village life that occupied Washingtonians along the Mall. Besides lectures and discussions by scholars of Indian history and culture, such as Ainslie Embree of Columbia University and Ralph Buultjens of New York City's New School of Social Research, there will be screenings of Indian films and performances -- such as poet Robert Bly reading his works to the spontaneous dance of Indian Bharat-Natyam dancer Neena Gulati. For more information about the Frostburg festival, call (301) 689-4221. Arts, Etc.

Nominations for the 1986 National Medal of Arts, now in its second year, are being accepted by the National Endowment for the Arts. The deadline is Nov. 8. Nominations should include a name, mailing address, telephone number and description of the nominee's accomplishments as well as reasons for the nomination and the name, address, telephone number and organizational affiliation, if any, of the nominator. Send to: National Medal of Arts, National Endowment for the Arts, 1100 Pennsylvania Ave. NW, Washington, D.C. 20506 . . . The Alvin Ailey American Dance Theatre travels to China Oct. 27, where it will work its magic in Peking, Nanchang and Shanghai before returning Nov. 11. The Ailey troupe is the first major modern-dance group to perform in China since normalization of diplomatic relations between the United States and the People's Republic . . . A new award has been established for writers. The Mrs. Giles Whiting Foundation, through its Writers' Program, has established a Whiting award of $25,000 each to 10 candidates annually; "special emphasis will be placed on exceptionally promising emerging talent," and the foundation will also consider "proven authors," says director Gerald Freund. The winners will be announced Oct. 31 in New York City . . . The Smithsonian Institution is ready for the mid-June 1986 flight of its remote-controlled replica of the pterodactyl Quetzalcoatlus northropi, the National Air and Space Museum announced last Thursday. The pterodactyl's creators have settled on an 18-foot wingspan.