Prince William County, known to most area residents as a place they pass through on their way somewhere else, has for years had the image of the defiant country cousin -- roughneck in its ways, and proud of it.

Even now, says one not-unhappy resident, "prince William is not a name you drop in McLean." Physically as well as socially it is one of the metropolitan area's "out counties" -- about 30 miles from the heart of Washington and almost an hour's commute at rush hour.

The county was notorious in the early 1970s for a raucous board of supervisors that, on its first day in office, axed the county administrator, planning commission and school board, then padlocked the ousted officials' doors.

Then there are scenes such as Sudley Road, the gateway to the center of the county. Called "Sullied" Road by its detractors, it is an unattractive, three-mile-long strip of gasoline stations, car dealers and fast-food restaurants. If you want to buy a corrugated steel toolshed, you go to Sudley Road.

Yet while the roughneck image persists, there are a number of signs that Prince William has left some of its wilder ways behind. For better or worse, the county is beginning to resemble Fairfax County, its rich, more sedate neighbor north of the Occoquan River.

"Oh, heavens yes, the county's image has changed a lot, and it's going to change more," says Ted Pugh, a salesman for the Coldwell Banker real estate brokerage firm. Pugh's employer did some of the market analysis for what will be Prince William's bellwether of Fairfax-style suburban expansion -- the county's first regional shopping mall.

The $60 million mall, to be built at the site of a new Dale City interchange on Interstate 95 in eastern Prince William, is expected to open in the fall of 1982. When the mall starts to yield an estimated $2.2 million a year in real estate taxes, the county sees an easing of recent -- and controversial -- budget cuts imposed to end years of what one former supervisor called "government by chaos."

"We have achieved stability," boasts Board Chairman Kathleen K. Seefeldt, whose deliberate style contrasts vividly with the rambunctiousness of her predecessors. "I would like to think our image has changed a lot in the last four years."

Six times the size of the District of Columbia, with one-fourth the population, now 150,000, Prince William for years drew thousands of blue-collar workers, lower-ranking federal employes and military people to its inexpensive housing clustered near the two interstate highways -- 95 and 66 -- that lead south and west from Washington.

Hidden pockets of poverty and substandard houses still dot semirural areas of the county, which reaches from the foothills of the Blue Ridge to the Potomac River and from southern Fairfax to the sprawling Marine Corpos base at Quantico.

But increasingly affluent new residents are buying expensive houses that used to be offered more frequently in Fairfax. And just as surprising, there are even previously unheard-of touches of class -- a county symphony orchestra and a reservations-only French restaurant.

At Evergreen Country Club, a subdivision near Bull Run Mountain in the western part of the county, the newest house -- custom-built with five fireplaces -- has gone on the market for $209,000.

In Dale City on the eastern side of the county, where the median price of housing has been in the mid-$50,000s, Hylton Enterprises has decided to market homes selling for about $92,000 to $110,000.

Charles Vincent, county director of construction services, said the starting price alone for most of the new single-family houses is now between $75,000 and $85,000.

"Some of it is inflation," Vincent Said, "but we're getting more expensive housing . . . Some of the houses even have saunas. The market seems to be there."

The money seems to be there, too, although there is disagreement about exactly how affluent the county has become.Sales Marketing and Management Magazine, in a recent survey of the region, put after-tax annual income of Prince William households at $27,524, only $434 lower than in Montgomery County, which has been on or near the top in family income in the area. Fairfax County's households earn an average of $30,169, the magazine says.

Although they are boosters of their county, Prince William officials say the survey's figures are too high -- perhaps by as much as 10 to 15 percent.

The word most often used by officials to describe the county has become "stability." Some examples:

The county has been able to halt all short-term borrowing. As recently as fiscal 1977, the supervisors were allocating $10 million -- or 12 percent of the budget -- to short-term debt.

In early August, the supervisors approved, 6-1, a $14.9 million bond referendum to go to the voters in November (when the supervisors' jobs are on the line). Only a few years ago, such a proposal would no doubt have been shouted down as frivolous.

There hasn't been an increase in the tax rate in three years.

The county's population growth has slowed from a dizzying 121.5 percent rate in the 1960s to 49 percent in the 1970s. In the 1980s, the growth rate is expected to fall even more -- to 40 percent.

The school-age population has leveled off years of rapid growth -- and even declined slightly this year.

Stability has not come without a price.

"What I could tell you would make you cry," says James H. O'Cain, executive director of the Prince William Educational Association, which represents county teachers.

"The county wants as many $11,000 teachers as it can get. You can imagine what that will do to the quality of eduction."

A teacher with one year's experience and a bachelor's degree makes $11,312 in Prince William, while the same teacher in Fairfax makes $12,990. In the past, lower housing costs in Prince William have offset the lower wages.

"While we straightened out our financial situation, someone has suffered -- and that's the public employes," acknowledges Supervisor James McCoart, who represents Dale City.

To help solve this problem, the county government is counting on new revenue sources -- on the regional mall and on industry, which is being courted by a newly created economic development office.

It is also counting on the increasingly affluent new residents who are buying the expensive houses that are part of the new Prince William.

While county officials are trying to cope with the changes, Luke Barzeger, the owner of La Chapelle, the only French restaurant in the area, is trying to bring sophistication to its food.

"What I'm trying to do," he says, "is bring back the days when things were prepared at the table -- chateaubriand, steak Diane. This is French service, it doesn't necessarily have to be French food." CAPTION: Pictures 1 and 2, Prince William is home to peaceful farms and busy Sudley Road Photos by Larry Morris -- the Washington Post. ;Picture 3, houses along Traveller Street in another area. Photos by Lucian Perkins and Larry Morris -- The Washington Post; Picture 4, George E. Alexander Jr., a systems engineer at the IBM assembly plant at Manassas, his wife, Lynn, and family. They paid $120,000 last year for a house near Nokesville in western Prince William. Photos by Lucian Perkins and Larry Morris -- The Washington Post; Map, no caption