Eighteen months after a special session of the Virginia General Assembly passed a groundbreaking package that included $421 million a year in new taxes for transportation improvements, traffic on Northern Virginia roads is as congested as ever, with drivers seeing little evidence that the windfall is being translated into asphalt and concrete.

Interviews with county officials, developers and civic leaders reveal a deep sense of frustration at the pace of highway improvements, which are viewed as the bulwark of continued economic prosperity in the region.

These critics contend that the state is hamstrung by bureaucratic practices and has yet to develop the sense of urgency needed to deal with an annual rate of traffic growth that approaches 12 percent on some Northern Virginia roads.

"In the legislature, everyone thought, 'Well, we've got the money and the problem has been solved,' " said Noman M. Cole of the Fairfax County Goals Commission, an influential citizens panel appointed by the Board of Supervisors to study growth in the county. "In all honesty, the problem hasn't been solved."

In addition, federal budget cuts in the highway aid program have forced the state to scale back several key projects in Northern Virginia, with more postponements likely, officials said.

Virginia Transportation Commissioner Ray D. Pethtel disputes the charge that the state has responded sluggishly to Northern Virginia's transportation needs, noting that bulldozers will begin to roll on many projects with the start of the construction season next month.

"This is the year that people will see all those orange cones, and what they'll be complaining about then is all the construction," he said.

Moreover, the state is exploring several new road funding strategies. Among them are the Rte. 28 tax district, which will assess commercial property owners in the corridor for some of the costs of widening the highway, and the possibility of allowing a private company to build and run an extension of the Dulles Toll Road from the airport to Leesburg.

Nonetheless, state officials concede, some of the most badly needed improvements have been tied up by engineering delays and money problems. Among them:The Springfield Bypass. Although design studies have been under way since 1976, most of the 35-mile road across Fairfax County has yet to move off the drawing board. Money has not been allocated for significant sections. In addition, because the state did not begin acquiring right-of-way until last fall, rising land values have inflated the cost of the project by more than $100 million. The extension of car pool lanes on I-95 (Shirley Highway) from Springfield south to Quantico. Viewed as the only practical relief for one of the busiest transportation corridors in the region, construction of the 19-mile car pool lanes was supposed to begin this year. But the loss of federal highway funds has forced the state to postpone the $172 million project for two years. Construction of car pool lanes on I-66 west from the Capital Beltway to Gainesville. A 1986 consultant's study warned that traffic in that corridor will double in the next two decades and recommended building "interim" car pool lanes on the shoulders until a more permanent solution is found. The loss of federal funds means that they, too, might be delayed, according to state transportation officials.

Northern Virginia's transportation needs are staggering. The county goals commission estimated that solving the area's transportation problems would cost $400 million a year for the next 10 years, or $4 billion -- a level far beyond current funding plans.

"Saying there's no money for it is like saying there's no oxygen when we all decide we have to breathe," said Edward M. Risse, cochairman of the transportation committee of the Fairfax County Chamber of Commerce. "It's very hard to catch up with 20 years of systematic deprivation. {State transportation officials} have, almost as a matter of policy, looked to transportation priorities elsewhere in the state."

Gov. Gerald L. Baliles promised to change all that. Under his administration, the annual allocation for road improvements in Northern Virginia has jumped more than fourfold, to $77.8 million in the current fiscal year, according to the Virginia Department of Transportation.

Last month, Pethtel announced the opening of a "full-service" district transportation office for Northern Virginia and the transfer of 20 employees from the department's Richmond headquarters, a move aimed at reducing engineering delays. A decades-old complaint from Northern Virginia is that the district office for the area was located in bucolic Culpeper, where the engineers did not have to face the daily reality of Beltway gridlock.

Moreover, at Baliles' request, top transportation officials have been meeting with Northern Virginia elected officials several days a month to develop a new blueprint for the region's transportation system.

"In the Northern Virginia district, we'll have 100 percent more projects {under construction} than we did last year," said Pethtel, who estimates that he spends 20 to 30 percent of his time on Northern Virginia issues. "There is just a tremendous amount of understanding that has to occur in a business as complex as transportation."

Much of the criticism has emanated from the Northern Virginia Transportation Alliance, a coalition of developers and business people formed during last year's election campaign for the Fairfax County Board of Supervisors. Alliance newsletters and press releases have continued to needle state officials on a range of issues, from the Springfield Bypass to the need for more autonomy at the district transportation office.

Developers, of course, have a compelling financial interest in spurring the state to move faster. More roads mean more land that can be turned into office parks, shopping malls and subdivisions. But criticism has issued from other quarters as well.

The goals commission charged that the state transportation department "has failed to provide effective planning, local design {and} road construction"; "failed to demonstrate any innovation for funding, implementation or ability to expedite improvements," and "lacks a sense of urgency in meeting the transportation crisis."

Shiva Pant, the Fairfax director of transportation, says that the state agency is "taking a lot of steps in the right direction, and we have to allow time for these initiatives to show what they can do."

But he added, "People are beginning to realize that money is sitting out there that has not been obligated . . . . We need to get some of these procedures simplified and get roads quicker, and the state has to come through."

The Springfield Bypass, which would traverse Fairfax County from Rte. 1 in the southeast to Rte. 7 in the northwest on a route roughly parallel to and outside the Beltway, has languished on the drawing board for more than a decade.

Final design plans for the road were not approved until June 1987, 11 years after the design process began. The state did not begin acquiring right-of-way until last fall.

Right-of-way acquisition for state projects typically does not begin until the design of a road is final, a practice that critics contend drives up costs. Soaring land values were cited last fall when the state revised the cost estimate for the Springfield Bypass from $250 million to $363 million.

In the meantime, money from a $135 million county road bond issue, most of it earmarked for the bypass, sat untouched.

The transportation department needs "to say, 'What are the shortcuts we can take?' " Pant said. He suggested that the state could have begun acquiring right-of-way for the bypass before completion of the design "with 99 percent certainty" that the land would be used for the road.

Thus far, the only completed section of the bypass, between I-66 and Rte. 50, was built by a private land developers John T. (Til) Hazel and Milton V. Peterson.

Another factor slowing the pace of road construction is the diminishing pool of federal highway funds. Under last year's federal highway spending bill, Virginia's share of federal highway money declined from $341 million to $245 million.

"Our worst-case scenario was $300 million," said Virginia Transportation Secretary Vivian Watts.

By delaying the extension of car-pool lanes on Shirley Highway, the loss of federal money also has created problems for a key segment of the Springfield Bypass. The car-pool project included the bridge that was to carry the bypass over Shirley, between Rolling Road and Beulah Street. Without the bridge, commuters on the bypass will have no direct access to Shirley Highway or the planned Franconia-Springfield Metro stop on the Yellow Line just southeast of Springfield Mall.

The transportation department, working with Fairfax County, is trying to find a way to build a truncated version of the car-pool project, perhaps extending the lanes for about three miles from their present terminus to Newington, the next major interchange, but even that will cost about $85 million.

"We're committed to expediting that project despite the loss of federal funds," Pethtel said.

Jack Hodge, chief engineer for the department, contends that the state is doing everything it can to speed construction of the bypass and other improvements. He said the state does not acquire right-of-way ahead of time because "if you wait until you have the design plans, then you know precisely how much right-of-way is needed."

Transportation officials point out that building a road is by nature a slow and deliberate process, requiring lengthy environmental studies and numerous opportunities for public review and comment. In the case of the Springfield Bypass, a colony of beavers built a dam that created a new wetland and forced a supplemental environmental review.

Nonetheless, state officials are sensitive to charges that they do not work hard enough for Northern Virginia. "So much of this is based on more than a decade of simply not having the funds," said Watts.

Despite such setbacks, the state is making some progress. Construction is proceeding on the $24 million interchange of I-66 and Nutley Street, which will improve access to the Vienna Metro station on the Orange Line. This spring, the state will complete the first phase of a $31 million widening of Rte. 1 through Crystal City. Work will begin soon on widening Braddock Road to four lanes between Guinea Road and George Mason University.

In April, construction will begin on the state's first section of the Springfield Bypass, between Rolling Road and Lackawanna Drive in southeastern Fairfax.

In the view of many transportation specialists, Northern Virginia's problem is at bottom a simple one: too few resources and a long legacy of neglect that goes back to the antihighway protests of the 1970s.

"It's a great irony," said one local transportation planner. "Ten or 15 years ago, {the transportation department} was being criticized for being a highway-building monster. Now everyone's turning around and saying, 'Where are those guys?' "