When Marie moved to Fairfax County from rural North Carolina eight years ago, she was optimistic about her future in the affluent suburban county.

Now, home for Marie is a small, government- subsidized hotel room on Fairfax County's gritty Rte. 1 corridor. She recently sent two of her three children back south to live with her mother because she was unable to support them on the $650 she brings home each month from her job as a cashier at a 7-Eleven. Marie has separated from her husband; she attended college for a year.

For Marie, who asked not to be identified by her full name, early optimism has been tempered by the reality of the high cost of suburban living. "I've been able to find a job. It's a better place to raise my kids," said Marie, but she added, "Life is hard here . . . . Everything is so expensive."

Marie is representative of what social service officials say is a growing population of poor people who are moving to Washington's wealthiest suburbs, lured by the abundance of jobs at restaurants, retail stores and offices and other opportunities created by the boom in suburban development.

In Fairfax County, about 50,000 people -- 8 percent of the population -- are living in poverty, according to a recent county study. But in a county of such overwhelming affluence, the suburban poor remain largely invisible.

"Poverty in Fairfax County is hidden," said Sandra Stiner Lowe, acting director of Fairfax's Department of Community Action, which compiled the study. "The pains of poverty are masked by fairly decent physical surroundings. What someone driving by doesn't see is that inside it may be infested with roaches, that there is no food, or that there are three families living in a place built for one."

In most cases, the face of poverty in the suburbs is far different than that of urban poverty, according to the Fairfax study. The report showed:About 60 percent of Fairfax's poverty-level population is employed, with the vast majority holding full-time jobs. "This doesn't fit the stereotype of the poor," said Lowe. "We clearly are not talking about people who are shiftless or too lazy to work." The level of education is relatively high. Of those living in poverty, 20 percent attended college, while 56 percent are high school graduates. The racial composition is diverse. About 47 percent of Fairfax's poor is white, 32 percent is black and the remainder is made up of other minorities. Blacks make up about 6 percent of Fairfax's total population.

Although the poverty in Washington's suburbs is less widespread than it is in the District, where almost a quarter of all households were classified as living in poverty at the time of the 1980 census, the increase in low-income families in the suburbs is substantial.

The number of persons living below poverty level increased more than 20 percent in Fairfax County during the 1970s, more than 30 percent in Prince William County and 16 percent in Montgomery County, according to the Metropolitan Washington Council of Governments.

At the same time, the level of poverty dipped slightly in the District.

Suburban social service groups say the trend has been reflected in increased demands on their programs. United Community Ministries Inc., a social service agency in the Mount Vernon area of Fairfax, reported a 70 percent increase in the number of people using its emergency food and shelter services.

"People have a tendency to move where the jobs are," said Verdia L. Haywood, deputy county executive for human services. "Low-income people also have the same set of values as everyone else . . . . They think of the suburbs as a better place in terms of quality of life, schools and open spaces."

While those opportunities are often greater in the suburbs, the economic burdens of suburban living are disproportionately high, especially in housing costs. The median value of houses in Fairfax County in 1985 was about $110,500. The average monthly apartment rent in Fairfax last year was $517, county figures show.

That is 54 percent higher than average rents in other major metropolitan areas of Virginia, according to a survey by the Tayloe Murphy Institute at the University of Virginia.

"Those people who are poor in Fairfax County are often much worse off than those in other areas of Virginia," said George Barker, a member of the Northern Virginia Coalition of Social Service Boards.

Federal housing assistance funds frequently are not available for apartments in Washington's suburbs because the rents exceed the allowed maximum, Baker said.

The cost of living is so much greater in the suburbs that Fairfax officials established a $15,000-a-year household income as the cutoff for those living at poverty levels, rather than the national poverty standard of just below $11,000 a year for a family of four. The median household income in Fairfax is $51,800 a year, according to county officials.

The high cost of rental housing is compounded by a shortage of rental units in Fairfax, where land is at a premium and developers have far greater interest in building up-scale houses and condominiums than traditional apartment dwellings, which low-income people can more easily afford.

County officials said waiting lists for subsidized housing in Fairfax average about 4,000 families, representing almost 11,000 people.

Although it is the Fairfax job market that attracts many low-income people to the county, many of those positions are in fast food and retail businesses that pay little more than minimum wage. After the high costs of housing, child care and transportation are subtracted, the jobs become much less attractive.

"We talk about there being so many jobs out here and no one to take them," said Sharon Kelso, director of Mount Vernon United Community Ministries. "The reason no one takes them is that no one can afford to take them."

The plight of the poor in the suburbs is a sensitive issue. Do wealthy jurisdictions like Fairfax, which provides free videotapes at public libraries and buys full-page newspaper ads boasting of the county's high number of PhDs, allocate resources to help those at the lower end of the income scale?

Some charge that the county does not.

"Fairfax tells us to go solve poverty," said Louis Carter of the Saunders B. Moon Community Action Association, an antipoverty agency in Fairfax's Gum Springs area. "Then they give us a penknife to fight a problem that requires a sword. They claim they are concerned about poverty, but it's a fake."

Carter argued that the county government's unwillingness to spend money fighting poverty is a reflection of larger attitudes in a community where many place a high premium on material success.

"People in Fairfax County think poor people are disgusting," said Carter. "It's not a matter of race. A poor white person is just as offensive as a poor black person. The attitude here is: 'I am doing well, so if you are poor, that must be how you want it.' "

"The county feels we're second-class citizens . . . . It's like we're poor relations," said Ruth Nesselrodt, president of the Mount Vernon Mobile Home Residents Association, who chides the county for delays in a redevelopment project at her trailer park. Nesselrodt describes herself as being of "comfortable income," but she said her trailer park is home to many low-income residents.

County officials reject the charge of callousness.

"It's totally unfair and unjustified," said Fairfax Board Chairman John F. Herrity. "We're not perfect, but, overall, the record is one of compassion and caring and trying to help, and we provide the resources to do it." He cited the county's plans to build shelters for the homeless.

Some antipoverty activists also come to the county's defense. "I find that people's eyes are very open," said Constance L. Pettinger of Reston Interfaith, a low-income assistance agency in Reston. "There has been a tremendous outpouring of support and sympathy for what we have been doing."

For people like Marie, however, the hardship of living amid Fairfax's wealth comes less from the scorn of others than from frustration at failing to match the standards around her.

"My children would come home from school and ask for money so that they could go on class trips," said Marie. "I work as hard as I can to give them what they want, but there was no way I could afford that."

Still, for all the hardship she has faced, it is the possibility of a better life that keeps her in Fairfax. "I feel that my chances are better here . . . . I would rather stay here and cope."