Soaring growth in Prince William County will soon require new roads, schools and other facilities totaling almost $700 million, an amount that far exceeds even the most ambitious estimates of Prince William's ability to pay, county officials said yesterday.

County Executive Robert S. Noe Jr., unveiling a list of "capital needs" that he acknowledged is too heavy for Prince William to carry and that will have to be pared significantly, called for a series of expensive spending measures, including $85.86 million in road improvements and other projects to be decided by voters at referendum this fall.

Bond referendums historically have been among the most divisive issues in Prince William politics, with voters rejecting nine of the last 12. Fiscal conservatives, motivated by a distaste for rising taxes and resentment of the county's growth, have already signaled skepticism regarding Noe's proposal and are expected to wage a full-scale campaign to defeat it.

Prince William's population has rocketed in recent years, making the once-rural county the second-largest locality in Northern Virginia. The result has been overflowing classrooms and county roads paralyzed by gridlock. More than 200,000 people now live in Prince William, and 100,000 more are expected by the turn of the century.

Noe's capital needs document, presented yesterday to the Board of County Supervisors, calls for $471 million in new roads, parks, and other county facilities over the next five years. School Superintendent Edward L. Kelly, meanwhile, has proposed spending about $220 million in his five-year plan for the county's 39,000-student school system.

The two wish lists total more than $691 million, which by some calculations is nearly four times the amount Prince William can reasonably afford if it pays for the projects through the issuance of bonds, considered the most likely funding method, county financial officials said.

"We have listed everything so that the community can know the totality of needs," said Noe, adding that he and Kelly will meet to trim their lists and devise a combined capital request to present to the supervisors.

Increasingly, Prince William's county government and school system have been in competition for the limited pool of debt that the county can prudently absorb. Prince William, seeking to ensure financial stability and instill confidence among those who purchase county bonds, has self-imposed limits on the amount of debt it can incur.

Those limits require that the county not incur debt greater than 3 percent of its tax base, and that it not spend more than 10 percent of annual county revenues to pay off its debts. If the supervisors refuse to bend the rules, the only alternative is to slash plans for new facilities, county officials said.

Early reaction from some supervisors indicated that they expect Noe and Kelly to do exactly that. "We're going to have to stay within our basic guidelines for debt," said Board Chairman Kathleen K. Seefeldt (D-Occoquan). "The big question is which projects can be deferred."

Although the supervisors lamented the approaching crisis over how to pay for new facilities, at least part of the problem is of their own making, according to county financial officials.

Seefeldt, for example, was among the board members who voted last year for a large election-year cut in the real estate tax rate, an action that resulted in the elimination of several projects from the county's budget. A substantial tax increase is expected during this year's budget sessions.

Noe's call for $85 million in bonds to be presented in one or more referendums this fall may be the most provocative element of the wish list unveiled yesterday. That would be by far the largest bond proposal ever presented to county voters, who have more often than not been hostile to the notion of debt financing.

Schools have been the exception, with voters approving $44.89 million in bond proposals last fall for new schools. A $42 million bond issuance to build roads and parks was defeated in November 1986, despite an aggressive campaign in its favor by county officials.

Road construction in Virginia has historically been the province of the state government in Richmond. Increasingly, however, Northern Virginia localities have been taking the burden on themselves.

Noe's proposed bond-financed projects include major improvements to Rte. 234 and Davis Ford Road, both heavily congested routes that connect Prince William's eastern sector with the western area around Manassas. Also in the proposal are two new public libraries, one at either end of the county, as well as a new training center for the police and fire departments, which was rejected in the 1986 referendum.

Staff writer Peter Pae contributed to this report.

--- PROPOSED REFERENDUM PROJECTS: WHERE THE MONEY WOULD GO ---

Prince William Parkway .............................. $22 million

Davis Ford Road design, right-of-way acquisition .... $20.6 million

Davis Ford Road (Parkway to Old Bridge) .............. $3 million

Rte. 234 third lane, ramp ............................ $2.6 million

Rte. 234 Bypass (Balls Ford Road to I-66) ........... $10 million

Police/Fire/Rescue Training Center ................... $8.65 million

Davis Ford Regional Library .......................... $5.38 million

Bull Run Regional Library ............................ $4.2 million

Recreation Center .................................... $9.43 million

Total ............................................... $85.86 million