The Fairfax Board of Supervisors said yesterday it doesn't have enough money to make all of the street improvements the county listed in the $30 million road bond referendum which voters approved three months ago.

The board's action confirmed what some county staffers said last fall: that $30 million could not possibly pay for all 14 projects the board selected prior to the November elections. The board had insisted all 14 be included in hopes of giving the bonds a better chance of passing.

Yesterday the board approved shifting $3.9 million of the road funds from 11 of the projects the voters approved to two other approved projects, the widenings of Gallows and Chain Bridge roads. In the process the supervisors said the county will have to ask voters to approve a second referendum this fall in order to complete all 14 projects.

The county's plan to build a toll road from Tysons Corner to Reston and Dulles International Airport is also facing financial difficulties, the board learned yesterday. The projected toll for the 10-mile trip has risen from 50 cents to at least 70 cents, and possibly as high as 85 cents, and construction approval from Richmond is not assured, county staff said.

Supervisors yesterday denied that the $30 million referendum had been misleading. They blamed their funding shift on the state highway department, which recently told the county that millions of dollars it earlier had allocated to Fairfax are not--and for at least two years will not be--available. Board Chairman John F. Herrity said the county may sue the state to obtain the previously promised highway funds.

"It's not a question of bad faith, unless it's the state's," Herrity said. "The highway department copped out on money that was available."

Although the board approved the $3.9 million shift unanimously, some supervisors, especially those whose districts did not gain by the shift, expressed misgivings. "Whenever our school board or anybody else goes out for a bond referendum, we are very careful and jump up and down and say you have to list your priorities and you have to stick to it," said Supervisor Marie Travesky, a Republican who represents the Springfield district.

Many supervisors regard congested roads and the state's inability or unwillingness to help improve them as Fairfax County's leading problem. The Virginia highway department is asking the General Assembly to approve higher gasoline taxes this winter to replenish its dwindling trust fund, but many Northern Virginia politicians say they will oppose any tax rise that does not give Fairfax and other growing counties a bigger share.

The supervisors stopped short of that position yesterday, but told county staff to study the construction formulas that various legislators have proposed. Last year the county convinced the General Assembly to permit it to sell road bonds, which led to the referendum and the county's first venture into road building.

County transportation officials suggested last fall that the referendum apply to four projects they were almost ready to begin, including those at Gallows and Chain Bridge roads. In a heated backroom session in September, supervisors insisted the list of projects be lengthened.

"If four or five members of the board have a hard time voting for something that has nothing in it for their district, how are you going to be able to go out and politic and get people to vote for $30 million in encumbrances?" Supervisor Joseph Alexander, a Democrat, asked then.

Since the referendum was approved, state highway officials have said it will cost more than they originally believed to turn Gallows Road from Route 7 to Idylwood Road into a four-lane highway. The estimate rose from $2.9 million to about $4.4 million.

The state also increased by $1 million its estimate for four-laning Chain Bridge Road from Dolley Madison Boulevard to Westmoreland Street and, in the move that angered the county most of all, explained that $1.4 million it had allocated to the Chain Bridge Road widening is not in the bank.

Northern Virginia highway administrator Donald E. Keith wrote in a December letter to the county that no new state projects will be initiated during the next two years on Fairfax's secondary roads. "Further from that date, we simply cannot predict at this time," Keith wrote.

The board voted to spend county funds on the two widening projects rather than wait for the state.

Meanwhile, the Dulles toll road, which the state also hopes to finance through the sale of bonds, is in danger because of high interest rates. Supervisors Martha V. Pennino and Nancy K. Falck and other county officials went to Richmond last week to try to salvage the project.

They said they still hope it will be built. But bond lawyers are studying how much the tolls would have to be to repay the $54 million needed to finance the road construction. The road would parallel the existing Dulles Access Road, which is owned by the Federal Aviation Administration and limited to airport traffic.