Virginia highway officials approved a route for the proposed cross-county Springfield Bypass yesterday that differs significantly from the alignment recommended in June by the Fairfax Board of Supervisors. County officials said the action may raise new questions about the fate of the proposed $180 million road.

The State Highway and Transportation Commission also took another step toward beginning a second major Northern Virginia highway project, approving location and design plans for a toll road to be built alongside the Dulles Airport Access Road.

The commission voted 10-to-0 to support a route for the Springfield Bypass that has three significant deviations from what Fairfax officials wanted. The modifications -- near a proposed government center west of Fairfax City, at Fort Belvoir, and at the Newington exchange with I-95 -- are likely to cause county officials to clash once again with the state's highway agency.

Construction of the 35-mile highway, which faces uncertain funding, would not begin until 1984 at the earliest, state officials have said. The bypass must still go through a design hearing -- when funds for the project are in sight -- to determine issues such as the number of lanes and the speed limit.

The bypass, also called the Springfield Parkway and the Reston Bypass, would traverse Fairfax County much like an outer loop to the Capital Beltway.

Under the plan approved yesterday, it would originate in the north at Rte. 7, Leesburg Pike, and snake south between Reston and Herndon, intersecting Barron-Cameron Avenue. Slanting slightly to the southwest, it would cross the Dulles Access Road and then curl around the western edge of Reston, crossing Fox Mill Road.

Continuing south, the bypass would cross West Ox Road to the west of Pinecrest and Thompson roads and then on to an intersection with I-66 and U.S. 50 east of Centreville.

The road would cross Braddock Road and the Southern Railway tracks just north of Butts Corner. From that point, the bypass would overlay Pohick Road and follow it to the intersection with Hooes Road where it would take a sharp turn to the northest and swing up to Rolling Road.

The bypass would then cut down to the southeast across I-95 and Backlick Road to Rte. 1 near Accotink.

The road is designed to provide better transportation for existing highways and improved access between major Fairfax growth centers.

Shiva K. Pant, Fairfax director of transportation, said yesterday he was disappointed with the changes in the bypass alignment made by the commission, and predicted that the county supervisors would "get into a dialogue with the highway department" because of them. "I don't think the board is going to sit back" and accept the commission's route, Pant said.

Pant acknowledged that the commission's route is identical to the county's for 72 percent of the road, or about 25 miles. But he stressed that the other 28 percent was the "guts" of the road.

"On the 72 percent," Pant said, "there was nothing else the commission could have done but what they did because of development. But in the remaining 28 percent, which were the guts of the project, there are significant differences."

The major differences between the county's recommendation and the alignment approved by the commission include:

The county planned to have the road turn sharply to the east at I-66, swerving to the eastern side of a proposed county government center, but the commission's road proceeds across I-66 and Rtes. 29-211 to the west of the center, roughly parallel to Stringfellow Road.

The county had requested that the road include an interchange with I-95 near Newington, but the commission vetoed the interchange, arguing that it would be too close to the existing Rte. 644 interchange at Springfield. State officials said that access to I-95 would be satisfactory under their alignment.

The county also favored a route that would intersect the proposed Franconia Metro station and then slice south down to Rte. 1, but the commission alignment provides only a spur from Rolling Road to the Metro station, with the bypass snaking to the southwest of Fort Belvoir to Rte. 1 near Accotink.

H.M. Shaver, the state location and design engineer who recommended the adopted alignment to the commission, said the changes were made so that "traffic would be better served" and more cars would use the road.

Shaver also said that the commission's route, at an estimated cost of $182 million, was $18 million cheaper than the county alignment.

But Pant termed any difference of that magnitude in the cost projections "academic."

"It will be up to the state highway department, not the county, to explain their rationale for the changes," he declared. But Shaver said that it is "possible, but highly unlikely" that the commission will change the route.

The commission also approved plans yesterday for two 12-foot lanes on either side of the existing Dulles Access Road, adding a $21.6 million bypass of the Tysons Corner area to the project. The Tysons bypass will allow motorists to go directly from the toll road to the new section of I-66 under construction inside the Capital Beltway.

The road, which has been previously approved by the state legislature, will cost a total of $55.1 million and be financed from the proceeds of a bond sale. Tolls would be set after the bonds are sold, but state officials said they have not set a date for the sale.

Beginning at the airport, the toll road will have interchanges at Centreville Road, Reston Avenue, Wiehle Avenue, Hunter Mill Road, Wolftrap Road, Rte. 7, and Spring Hill Road.