The new Fairfax County Board of Supervisors -- moving immediately to address the issue of transportation that dominated the November elections -- voted unanimously yesterday to plan a $150 million spring road bond referendum that would be the largest ever for the county, and it advanced a host of other initiatives to speed road construction.

The bond referendum was proposed by Audrey Moore, the board's new chairman, and was tentatively scheduled for April 12. Voter approval of the bond issue would be a major step toward financing what county officials estimate is $4 billion in road improvements needed throughout Northern Virginia in the next decade.

Although a list of Fairfax projects to be funded by the bonds has not been drawn up, officials said the money likely would be used to pay for segments of the Springfield Bypass, intersection improvements, road widenings, commuter parking lots, and land acquisition for roads and facilities such as county garages.

A public hearing on the proposed referendum is scheduled for early next month, after which the board will take its final vote.

In a meeting dominated by transportation issues, the board was briefed by Ray D. Pethtel, the state transportation commissioner, who promised a new commitment to cooperation between the county and state governments. This was symbolized by his announcement that the state will establish a full-service regional office in Northern Virginia.

"This is the year of moving dirt," Pethtel said.

In addition, the Fairfax board approved a measure designed to speed the process of acquiring land for major road projects such as the Springfield Bypass, the 35-mile cross-county highway between Rte. 1 in the southeast and Rte. 7 in the northwest. State and county officials said they have agreed to accelerate the design and construction of the bypass so that two major sections could be completed as early as 1989 -- two years ahead of schedule.

"We've reached a new understanding of how we're going to work together," Board Chairman Audrey told Pethtel. "We very much appreciate your cooperation in getting that asphalt on the ground and making that money go further."

Moore, a Democrat, was in charge of her first meeting since she and three board newcomers were elected last fall in a bitter contest that turned largely on promises to unclog the county's road network. Relations between the state and county have long been strained by accusations that Richmond has not been adequately responsive to transportation needs in fast-growing Northern Virginia.

Pethtel and Moore seemed determined to put those days behind them. "The posture of the department now is: If we make a promise, we're going to keep it," Pethtel said.

Yesterday, relations between the supervisors were not all so congenial, however. Supervisor Elaine McConnell of Springfield, who as a Republican is now in the minority, chafed under the loss of her board-appointed position to the Northern Virginia Transportation Commission. "Bipartisan interests are no longer being represented," she said, calling the loss of her place on the commission "a power move, a political move to show that the Democrats are in control."

Moore dismissed the allegation, saying, "The appointments I made had to do with the interests of the particular individuals and where they could best serve."

Cooperation alone will not solve Northern Virginia's transportation needs. State and county officials in recent months have expressed concern about the loss of federal highway funds as well as steadily rising cost estimates for major road projects. Last fall, for example, the expected cost of the Springfield Bypass was increased from $250 million to more than $350 million.

If passed, the bond issue would cover part of that difference. Under the measure passed yesterday by a 9-to-0 vote, a public hearing on the referendum would be held Feb. 8 and a special election on the bond issue would be conducted in April. The election date could change, however, because of a technicality in state law that prohibits a referendum less than 60 days before municipal elections. The towns of Vienna, Clifton and Herndon hold their town elections in May.

Bond referendums in Fairfax traditionally have done well. Voters have approved $190 million in road bonds in the three referendums since the county acquired the authority to issue road bonds from the General Assembly in 1981. In fall 1985, voters approved a $135 million bond issue, $85 million of which was slated for the Springfield Bypass.

County Executive J. Hamilton Lambert said that this year's road bond referendum, which would cost an estimated $300,000 to put on the ballot, would not interfere with plans to hold school and park referendums and possibly a human services bond referendum in the fall.

In a related matter yesterday, the board voted to establish a 10-member Transportation Advisory Commission to explore other ways to finance roads, such as through sales tax increases, land transfer fees and property tax increases.

Also, the board approved a new financing mechanism that would allow the county to use existing, unsold road bonds to acquire rights of way for major roads before the design process has been completed. That allows the county to buy land before it can be developed, a problem that has been cited as a reason for the rapidly rising cost of the Springfield Bypass.

Specifically, the measure releases $9.1 million to acquire property along the paths of five road projects, including the bypass.

State and county officials said the beefed-up state transportation office in Northern Virginia could significantly reduce the amount of time it takes to translate highway blueprints into paved road. "They're not just moving the people up here," said county transportation director Shiva Pant. "They expressed the commitment to give those people power to make decisions that used to be made in Richmond."

Pethtel pledged to speed the process of building the Springfield Bypass, one of the area's transportation priorities. Officials hope to speed construction on two sections, between Rte. 50 and West Ox Road in the northwest and between Beulah Street and Rolling Road in the southeast, where the bypass crosses I-95.