In an effort to unclog traffic on the Dulles Toll Road, Virginia highway officials announced plans yesterday for a flash pass system that would allow commuters to bypass coin-operated toll gates and the long lines that often form behind them.

The announcement came as Virginia Gov. Gerald L. Baliles led a bus tour of highway construction sites in Northern Virginia, an event timed to coincide with the anniversary of the $422 million transportation tax package pushed by Baliles and enacted by the General Assembly last September.

In a speech at George Mason University, Baliles expressed frustration with the cumbersome process of planning, designing and building new highways and called upon local governments to create a regionwide transportation plan in the next two years.

"We've got to find a way to cut the time it takes to build a road," Baliles said. Referring to the long list of speakers who signed up to address the gathering, Baliles added, "I am concerned that we may have so much transportation planning that we will end up with all planning and no transportation."

Baliles also announced plans to spend $3.8 million to synchronize traffic signals in Virginia, a project of particular consequence in Northern Virginia, which has more than half the traffic signals in the state. In addition, Baliles said, the state plans to spend $1.5 million for a computer-based traffic signal system in Fairfax County, which he said would save Northern Virginia residents nearly 350,000 gallons of fuel a year.

The half-day transportation extravaganza, which included an elaborate lunch for about 200 transportation planners, state officials and politicians, comes at a time of mounting pressure on public officials to do something about traffic congestion in Northern Virginia.

Tuesday, the Northern Virginia office of Peat Marwick, an accounting firm, released an analysis of highway construction in Fairfax County since 1975, when the county completed its master transportation plan. According to the study, the county has completed or is building just 123 miles of lanes, or 21 percent of the 600 miles of freeway and secondary lanes that were laid out in the transportation plan.

Virginia officials went to considerable lengths yesterday to describe the extent of highway construction in the region.

Accompanied by charts and slides, Transportation Commissioner Ray Pethtel described how the special tax package has increased primary road spending in Northern Virginia to $26.5 million in the current fiscal year, more than five times the amount that would have been spent had the package not been passed. Secondary road funding, he said, has increased four times, from $8.9 million to $37.6 million.

Pethtel noted that 72 highway construction projects are now under way in the Northern Virginia transportation district, compared with 16 in 1985. "I believe that the future of transportation is brighter in Northern Virginia than ever before," he said.

Of more immediate benefit to most local motorists, however, were the plans announced for the Dulles Toll Road, where long backups at the main toll plaza are a regular feature of weekday rush hours.

Under the experimental flash-pass program, motorists who pay $66 every three months will be issued a colored metal plate to fasten beneath their license plates. The pass, which officials view as a precursor to an electronic toll collection system, will allow commuters to drive through a new express toll lane without stopping to deposit change or wait for a gate.

The passes will be good only during rush hours at the main toll plaza. The program is scheduled to begin on Jan. 4, 1988, if additional lanes are completed on time.

Despite the generally cheery tone of the day's events, Baliles acknowledged frustration with the pace of transportation progress in Northern Virginia.

"Too often, conflicting so-called official reports are simply used as a rationale for delay," he said in a speech that echoed the complaints of some Northern Virginia developers. "Meanwhile, the costs of rights-of-way, which frequently absorb half the cost of construction, continue to skyrocket."

To speed the planning process, Baliles proposed that state transportation officials meet monthly with Northern Virginia elected officials and transportation planners to create a "detailed, official transportation plan -- a map, if you will."