Alexandria is gambling $10,000 to try to bring to life a 10-year-old plan to build a new interchange on the Capital Beltway, a project that city planners say is crucial to the development of its industrial zone along Cameron Run.

This week the City Council voted to spend the money on an impact study that is not required by any law or agency but which the city hopes will help persuade state and federal officials to approve the project.

In 1981, the Virginia Department of Highways and Transportation turned down the interchange, which would be built at Clermont Drive, contending it would be too close to existing interchanges at Telegraph Road and Van Dorn Street and would heighten congestion on the heavily traveled Beltway, designated Interstate 95 at that point.

But after lobbying from legislators and state Highway Commissioner Joseph Guiffre, the state is rethinking the decision. Even if the project gets state backing, it still would have to obtain federal funds to cover most of the estimated $3 million cost.

Dayton Cook, Alexandria's transportation and environmental services director, is optimistic. "We know where we're going," Cook said. "It's just a matter of when we get there."

The diamond-shaped interchange would channel traffic between the Beltway and a four-mile strip parallel to the Beltway between Van Dorn Street and Rte. 1, which Alexandria hopes to fill with offices, warehouses and factories.

The city has spent millions constructing the zones' main road, Eisenhower Avenue, and building flood control works on Cameron Run. It has succeeded in drawing major clients to the area, such as the American Trucking Associations, Inc.

Poor access to the interstate system--a big concern for companies considering a move--continues to hamper development, city officials say. The industrial strip is bounded on the north by tracks owned by the Richmond Fredericksburg & Potomac and Southern railroads and on the south by the Beltway, with few ways across them. The Beltway exits are relatively distant and congested.

Clermont Drive runs beneath the Beltway with no access to the lanes above. At the RF&P railroad tracks it narrows to a single-lane underpass. Nonetheless, every morning rush hour about 1,000 vehicles coming north from Fairfax County crowd their way along Clermont Drive into the industrial zone.

In 1973, Fairfax County and the city established the Beltway as their common border, replacing Cameron Run. The county gave its approval for an interchange at Clermont, provided that access into Fairfax County was closed off. The county said it did not want the resulting heavy traffic to pass through residential areas that border the Beltway.

The new interchange would take pressure off the interchanges at Van Dorn and Telegraph Road and eventually channel 20,000 commercial and commuter vehicles in and out per day, city officials say, accelerating development in the zone. "That's Alexandria's tax base for the next 20 years," Cook said.

Interstate projects normally are funded 90 percent by the federal Highway Trust Fund and 10 percent by the state. Alexandria officials have indicated, however, that the city could put up some or all of the state's 10 percent in this case.

In 1981, the state opposed the project. "We did not think that 95 can accommodate another interchange, due to the traffic congestion that this would cause," said Don Keith, the highway department's division administrator for Northern Virginia. Keith said the department now has an open mind.

The city also faces opposition from citizens over a related proposal to extend Clermont through to Duke Street. Bernard Brenman, secretary of the Holmes Run Park Ad Hoc Committee, a group of citizens associations in the Duke Street area, says the new road would damage the environment.