When Metro's Orange Line first opened in Arlington three years ago, owners of small businesses in the county's decaying downtown hoped the subway would bring them new customers.

Now, many fear it could bring them ruin.

They are people like Jeffrey Gunther, an antique dealer who is paying almost twice what he did last year to rent a shop facing the Clarendon station; Ratri (Lucky) Friend, who worries that rising rents could force her to close her hair salon at the Courthouse stop; and Lee Russell, who recently moved his Ballston area food market from its location of 40 years rather than accept a one-year lease at twice the price.

"Within a few years, there won't be any more small businesses. It'll be a thing of the past," said Gunther ruefully.

"Eventually it'll all be shopping centers. That's what they call progress."

For about 300 other owners of small businesses along the county's Rosslyn-Ballston corridor, the opening of the Metro line has meant an ever-tightening economic squeeze. Commercial property assessments between the Courthouse area and Ballston, fueled by the promise of Metro-related development, skyrocketed over last year at a time when overall county assessments stayed virtually level.

That has brought higher and higher rents for the shopkeepers, most of whom rent their retail space. At the same time, landlords are offering shorter and shorter leases, often as short as a year, in hopes of keeping their options open in the game of Metro development.

It all means that the shopkeepers, most of whom have been in business for years, could be the first to go when building owners decide to replace their low-rise shops with high-rise developments. County officials expect that to start happening within about five years, as developers begin work on the millions of dollars worth of construction projects that have already been approved for the corridor.

A recent Chamber of Commerce survey of small businesses along the corridor found that most have less than two years left on their leases. Some 30 percent said they expect to have to move as a result of redevelopment, while another 20 percent said they did not know.

Those fears, say county officials, are real yet difficult to address. "The unfortunate fact, and we've seen it happen in the District, is that redevelopment drives up prices and drives small business out," said county economic development official Diana Wahl, who said the county is looking for ways to assist the businesses.

A regional government loan guarantee program, for instance, is expected to help a few of them relocate.

Yet, a recent request by a Vietnamese business association for a $35,000 study of redevelopment issues in the Clarendon area was rejected when county officials said the request was too vague. "We know there's a problem, but we haven't come up with a solution," said Joanne Jackson, a business development specialist for the county. "It's been all support but no money to this point."

That offers scant comfort to Ratri (Lucky) Friend, a Thai woman who has seen her rent go up more than 30 percent since she opened her "Hair Friend" salon near the Courthouse stop two years ago.

"I thought it was a good location across from the Metro, but Metro hasn't helped me much," she said as she surveyed her empty salon. "People have to run real quick to get on the Metro, and they don't want to stop . . . If it gets too expensive and I can't afford it, I'll just have to quit."

County tax figures offer a dramatic indicator of the corridor's changing economics.

While overall county assessments went up only 0.4 percent last year, commercial real estate in the five census tracts abutting the Courthouse, Clarendon, Virginia Square and Ballston stops rose an average of 17.9 percent over 1981.

In the Courthouse area, which has two major construction projects underway and two more on the drawing board, commercial assessments went up an average of 28.2 percent. Some properties are now valued at up to 60 percent more than they were last year.

The reason, says county tax assessor James R. Vinson, is obvious: "When you look at a map of Arlington and see where the major development is going to occur, it's almost always within walking distance of a subway stop. And when an area begins to get new development, it becomes more attractive to other developers."

County officials say they expect landowners to wait out the economic downturn while jockeying to assemble land parcels large enough to qualify for dense development rights. Then, when the big projects begin to go up, the exodus of small businesses will begin.

"It's a real tough problem," said David Guernsey, chairman of the chamber's small business subcommittee and president of an office supply store that rents space in the Clarendon area.

"On the one hand, you know the area's got to be redeveloped because it's deteriorating, but on the other hand you don't want any casualties--especially if they're innocent victims."