St. Charles, a new town that quietly gained momentum during the 1970s, is poised to become the major business and center of sparsely inhabited, mostly rural Charles County, Md., in the 1980s.

"We're not as big nor nearly as well-known as Reston or Columbia," said Charles E. Stuart, president of Interstate St. Charles Inc., developer of the 8,000-acre community. "But we are achieving both a local and an area-wide identity -- not just as a place where moderately priced new homes are available -- but also as a new town that has industries, businesses, services and public recreation."

Stuart and his development team prefer not to mention that the growth of St. Charles, which has a population of 13,000; has been hindered by its location in Southern Maryland, 15 miles southeast of the Beltway.

There are no other major population centers in Charles, St. Mary's or Calvert counties, which make up the Southern Maryland peninsula.

Like the Washington region's other large new towns, Columbia and Reston, St. Charles is about 25 miles from the White House.

The larges new town, Columbia, has 16,000 acres and has grown the fastest. One reason is its location on major corridors midway between Washington and Baltimore.

Reston's 8,000 acres are on the northwestern fringe of burgeoning Fairfax County near Dulles International Airport. It is also not far from Tysons Corner, a growing office and commercial center some regard as the unofficial capital of Northern Virginia.

Not as well known as the other new towns, St. Charles has not attracted as much heavy industry or as many residents and businesses.

While the small development team planning and activating the growth of St. Charles may have a complex about location, there's no inferiority complex. Stuart said that 800 new dwellings were built and occupied in St. Charles in 1979, up from 500 in 1978 and 360 in 1977. But those were big years for housing everywhere.

"We cannot deny that sales and traffic died in the latter months of 1979 due to mounting interest rates," Stuart acknowledged. His development projection for 1980 includes 500 new dwellings in the town.

"We are confident that we'll get our share of a diminishing area market and we have a mix of semi-detached, town houses and single houses priced from $43,000 to $85,000," he said. "That should keep us in the affordable housing range."

Additionally, St. Charles has become the apartment center for its area. There is a mix of 600 occupied rental units, ranging from subsidized apartments for low-income renters to market-rent units; 400 more are under construction.

"Our planning and policy are such that you can't tell the rent subsidy or subsidized units from the market-rent apartments," said Jay Parker, full-time consultant to St. Charles for the planning-architectural firm of O'Donell & Henninger Associates Inc.

Eleven home-building firms, some of them new and quite small are building houses lots in St. Charles that now cost the builders at least $17,500. Of the current builders, Pulte Homes is the biggest producer. Ray Smith, president of Pulte's eastern Maryland division said the firm has sold 695 houses there in the past six years.

Increased costs of development and general inflation have pushed up land costs in recent years, Smith said.

"Now we have to build more expensive houses and the selling pace slows," he said. St. Charles has certainly become an identifiable, attratice place. Location is the only real negative factor. We look for sales to bounce back this spring, expecially for town houses and duplexes."

The Ryland Group and U.S. Home (formerly Page Construction) built earlier in St. Charles but never achieved high production levels. Washington Homes Inc., which began building in the first section of St. Charles in the late 1960s, is finishing a final section of town house in the community's first completed neighborhood.

Basically, St. Charles was planned as a complex of five village centers -- each with 15 small neighborhoods. Currently, St. Charles is building its first major village center (Smallwood) where Post Office Road merges into St. Charles Parkway.

That low-rise, 9 million center on 110-lakeside acres will have 153,000 square feet of retail, office and medical space, a new library, a school, a park, a church and fire and police center. All of the retail stores, anchored by a large Safeway and a People's Drug store, will face outward from a service area center.

"There will be no theater or any pinball arcade," said Tod Hullin, vice president for commerical development. He said that the village center scheduled to be open early in 1981, will be within easy walking distance of residents of nearby apartments and houses.

Hullin said that plans are moving for a 1980 start on a regional shopping mall that St. Charles has long wanted to have on the west side of Rte. 301. A 101-room Holiday Inn already is operating there.

The regional shopping mall will initially have 330,000 square feet of space, including a branch of Almy, a New England-based department store chain.

The entire St. Charles community will not be completed until the end of this century. By that time it is expected to have nearly 70,000 residents in five villages -- equal to the present population of Charles County.

Aided by $38 million in federally guaranteed loans, St. Charles has built roads and lakes, developed an industrial park and given ground to the county for the 200-acre White Plains park.