Arlington County is betting that Metro's multi-million dollar Orange Line, scheduled to open at four stations Dec. 1, will trigger major changes in an aging, five-mile suburban corridor in decline for the last 20 years.

The steeply climbing prices on deceptively modest-looking homes in neighborhoods near the stations already indicate that county leaders may have won their wager.

"Metro is placing trememdous demand on residential real estate," said George Mason Green Jr., who has sold homes in the corridor neighborhoods of Parkington, Clarendon, Virginia Square and Ballston for the last two decades.

Price tags of $93,000 -- the average cost of an Arlington home, according to recently compiled figures -- and up to $200,000 in Lyon Village, a neighborhood near Clarendon, have failed to discourage homebuyers lured by the promise of fast Metro subway service to and from downtown Washington.

Although spiraling interest rates and other financial uncertainties have slowed sales recently, Arlington real estate salesmen report that housing prices in the neighborhoods surrounding the stations are 70 percent higher than they were four years ago.

"We're seeing a tremendous demand by young, two-career couples who until recently would have bought in Georgetown or Capitol Hill," said Green. "Now they compare prices and look at Arlington's location and its low tax rate."

One young Washington lobbyist and his wife, a federal employe, already are committed to leaving the District for Arlington, drawn there by the soon-to-open Orange Line.

"After we'd been broken into several times on Capitol Hill I wanted to leave the District, but my wife loves the city," said the lobbyist, who asked not to be identified.

"We agreed to move to an area where we could walk to the subway. We got a map and drove around each stop in Arlington and after a month of looking, bought a house in Lyon Village."

They paid $145,000 for a five-bedroom, Tudor-style home and plan to move in shortly after the Orange Line is extended.

What Metro has done for Arlington real estate without even opening, county officials hope it eventually will do for commercial redevelopment in an area that hasn't seen good times since the late 1950s.

Newspapers blow through the windswept walkways of Parkington, a 27-year-old, pea-green shopping mall located at the end of a shabby, five-mile commercial stretch of Wilson Boulevard. The center, like most of the Wilson Boulevard corridor, was eclipsed long ago by the flashier stores at Tysons Corner and other nearby malls.

Last month, executives of the St. Louis-based May Department Stores, which owns Parkington, unveiled a $100 million redevelopment plan, calling the surroundings a "super-viable area" largely because of the Ballston Metro stop two blocks away.

Within the next two months Arlington officials will decide whether to contribute $13 million toward the effort, an expenditure May Co. officials have set as a precondition for renewal.

"The subway is going to make all these areas just an extension of downtown," said Arlington planner John Gessaman. "The renewed interest we've seen this year is almost all due to Metro."

In addition to the Parkington proposal, there are other signs of renewed interest traceable to Metro:

Mobil Corp., the owner of Colonial Village, a 55-acre, 1,100 unit garden apartment complex close to the Courthouse station, the first stop on the new line, has announced plans to convert the project to a mixture of condominiums, cooperative apartments and office towers.

Two other moderate-cost garden apartment projects near the Courthouse Station, Arlington Courts and Courthouse Gardens are slated for demolition. If plans are approved by the county board, they will be replaced by high-rise office buildings and a condominium.

Building permits for the first quarter of 1979 were up 100 percent over last year, according to Chamber of Commerce executive director Norman C. Worthington. "Today the market is for office space," Worthington said, "Because of Metro there is a very definite feeling of optimism in the business community."

Trustees of George Mason University Law School, located in the former Kann's Department Store two blocks from the Virginia Square station, plan to build a major educational center on the 11-acre site the school owns. "That's one of the prime pieces of real estate in the metropolitan area," said trustee John T. (Til) Hazel Jr., who grew up near there and remembers it as "good squirrel-hunting country."

"There's more money to be made in that corridor than in any part of the U.S.," said Preston Caruthers, a prominent Northern Virginia developer who in the early 1970s began assembling sizeable parcels of land around the stations. Current land-use policy in Arlington calls for centering high-density development around Metro stations. "There just isn't any more land in downtown Washington, Rosslyn or Crystal City," said one county planner. Land prices in Ballston, he said, are currently about $30 per square foot, half what they would be in Rosslyn, and one tenth of the going rate in downtown Washington.

Caruthers predicts that the area will undergo "slow, steady growth" in the next decade. "The problems you face are those in any redevelopment," he said. "You're a pioneer. What potential investors see in Ballston is radiator shops and falling down houses," not the large vacant tracts found in Fairfax and Montgomery Counties.

"There's one good thing about the depths to which we've plunged, and that is that people want change," said planner Thomas Osborne.

The planners, including Osborne, say they don't want to duplicate Rosslyn, a financially successful high-rise office development that has been sharply criticized as an aesthetic disaster.

Osborne noted that other station areas have aesthetic problems, too. "We've done a god-awful job around the Courthouse," he said. "The county buys land and parks on it, so what you've got is eight acres of gravel parking and chewed-up asphalt. It's not much of a government center for an urban community."

"Arlington has been built once," said developer James H. McMullin, chairman of Arlington's Economic Development Commission. "What redevelopment in Arlington means . . . is that many of these old facilities have to be torn down."

Some officials point out that razing buildings for redevelopment also causes other problems, chief among them displacement of tenants whose apartments are demolished.

"Part of what must be considered in redevelopment is how to prevent low- and moderate-income people from being wiped out in the process," said housing services director Edward B. Brandt. In the last few years, he said, 25 percent of Arlington's once-abundant stock of moderate-cost housing had been lost to condominium conversions.

Yet another unsolved problem is parking.

While the Arlington County Board has given approval to temporary parking lots around the stations, officials are braced for traffic hassles. The Orange Line extention is expected to add about 10,000 Metro riders to the system, an undetermined number of whom will drive to the stations and park on nearby residential streets.

"No matter what you do it's going to bring in more cars," said county public works director Henry S. Hulme, who predicted that the Ballston area, with its narrow streets, will be worse than Rosslyn during rush hour, as more than 100 buses an hour pick up and discharge passengers.

Because of the way the county's permit parking law is written, residential parking bans cannot be instituted in anticipation of a problem, only after one develops.

"We're very worried about parking in the neighborhood," said Planning Commissioner Katherine Freshley, a Ballston resident. "The reaction here is panic. I think the first month Metro is open people will be screaming for street barriers. Nothing destroys a neighborhood more than through traffic."