Montgomery County, home to an increasing number of racial and ethnic groups, will sponsor a daylong Ethnic Heritage Festival at Wheaton Regional Park Sunday.

The festival, which runs from noon and 7 p.m., will feature a variety of foods, music and dances, a giant birthday cake marking the 350th anniversary of Maryland's founding, a hot-air balloon launch and crafts.

County officials said they expect thousands of people to attend the festival.

Parking at the park itself will be limited to handicapped persons. Free shuttle buses will run continuously from 11 a.m. to 8 p.m. between the park and these locations: the Viers Mill Road commuter lot at Wheaton Plaza; the Ride-On bus lot at the Silver Spring Metro station; John F. Kennedy High School, 1901 Randolph Rd., Silver Spring; Holiday Park Multiservice Senior Center, Connecticut Avenue and Viers Mill Road; Richard Montgomery High School in Rockville; the GEICO parking lot on Western Avenue, Chevy Chase; and Gaithersburg High School, 314 S. Frederick Ave.

For more information about the festival, call 251-2500.

Tribune-United of Montgomery County is scheduled today to open a store in Rockville that will allow prospective customers to view cable programs before buying the firm's television services.

A Tribune-United spokeswoman said the opening of the store at 807C Wintergreen Plaza marks the first time a major cable company in the Washington area has provided consumers with such a storefront service.

Cable subscribers in Montgomery will be able to pay their bills and sign up for additional services at the store. The store also will have more than a dozen television monitors showing the various programs Tribune-United will provide as it wires Montgomery for cable.

Montgomery's Office of Information and Volunteer Services is sponsoring a photographic art contest for local camera buffs who have taken pictures of "traditional, beautiful spots in the county," a spokesman said.

Interested photographers -- contest rules require them to be Montgomery residents -- should submit 8-by-10-inch glossy black and white photos of county scenes by Sept. 14.

Winning photos will be distributed to local libraries, government agencies and other organizations, a county spokesman said.

Entries should be mailed to the Montgomery County government, 101 Monroe St., 3rd Floor, Rockville, Md. 20850.

The average per capita income in Montgomery County was $18,212 in 1982, 64 percent higher than the national average but only 14th in a ranking of jurisdictions nationwide.

A recent survey by the U.S. Commerce Department also found that Montgomery's average per capita income ranked fourth in the Washington area, behind Falls Church ($19,909), Alexandria ($18,896) and Arlington ($18,765).

The combined personal income of all Montgomery residents totaled nearly $11 billion in 1982, according to the Commerce Department's "Survey of Current Business."