Virginia Gov. Gerald L. Baliles, beginning a four-day stay in the Washington suburbs, announced yesterday that he had directed the state highway department to begin adding a third lane in each direction to the two-year-old Dulles Toll Road.

The move was one in a series of actions that the governor said he had taken to relieve the increasing congestion on Northern Virginia highways.

Shortly after arriving at Alexandria's Amtrak station on a special train filled with state officials, the governor said he had:

*Approved a crackdown on unsafe and speeding trucks, especially on the Capital Beltway.

*Directed that all State Police cars be equipped with "push bumpers" that will allow them to shove stalled vehicles off the highways quickly without having to wait for tow trucks.

*Begun a police motorcycle patrol unit to work the region's interstate highways to give troopers "the capability to reach traffic-delaying situations more quickly."

*Reached a tentative solution to an insurance problem that has delayed the start of an experimental commuter train between Fredericksburg, Va., and Union Station in Washington.

The governor, who zigzagged to various stops across the Washington suburbs in a police-escorted motorcade, also paid attention to other issues. At Dulles International Airport he welcomed an announcement that Presidential Airways and Pan American World Airways have agreed to pursue construction of an eight-gate passenger terminal there.

Baliles toured two temporary midfield terminals there, welcomed United Express, a new air service, and participated in the announcement by Dulles-based Presidential that it has signed a three-year joint marketing agreement with Pan American.

James A. Wilding, director of the federally owned Dulles and National airports, told the governor and his delegation that major construction will have to begin "within a couple years" of the proposed transfer of control of the two airports to a regional airport authority.

Ultimately Dulles could be "Atlanta-like," Wilding said, referring to the major regional airport in the Georgia city. Such growth will mean acquiring 900 more acres for a fifth runway, he said. It also assumes Congress will approve the controversial transfer measure.

"That's what the transfer is all about," Wilding said.

While at Dulles Baliles also promised that construction will begin within 45 days on special ramps to allow commuter buses from the Reston area to use the less-congested Dulles Access Road, which parallels the often congested toll road.

Traffic on the toll road, opened 20 months ago, has far exceeded projections and toll revenues are "substantially above what is needed to pay off the bonds that built the road," the governor said.

Traffic between Leesburg Pike and Hunter Mill Road, the governor said, is running more than 48,000 cars a day -- double what was projected.

Baliles said he had asked state Transportation Secretary Vivian Watts to "take the first step in the process of expanding the capacity" of the highway and promised that expansion of the highway will incorporate "the concerns of the communities along that corridor."

Earlier, as he traveled from Richmond on a four-car private train, Baliles said a public-private partnership "with a little luck" might enable the long-stalled commuter rail pilot project to begin operation by the end of the year. Under the plan, the Richmond, Fredericksburg & Potomac Railroad, over whose tracks the trains would run, will ask its London insurer to include the commuter service under its liability policy.

At Baileys Crossroads, Baliles got a demonstration of space-age technology at TRW's new federal systems group. TRW officials fed highway statistics into a computer program normally used for space surveillance and missile warnings, to show the impact of the construction of a Washington bypass on the Beltway.

Even with such a new outer beltway, the computer found that traffic on the existing Beltway would increase dramatically by 2005. Without the new road, the computer blinked red warning signals that translate into gridlock.