In a sneak preview of the clash that seems likely to recur in the General Assembly session starting in January, Fairfax and its suburban allies challenged rural interests today on what has become one of the state's most divisive issues: How to pay for the massive improvements needed in Virginia's road network.

At the annual meeting of the Virginia Association of Counties, Northern Virginia and its suburban allies, breaking with the state's "pay-as-you-go" tradition of financing new roads out of current funds, have proposed a statewide road bond of at least $500 million. Rural counties, wary that they would help pay for but see little benefit from the bond, generally opposed it.

The proposal also brought immediate scorn from A.L. Philpott (D-Henry), the powerful speaker of the House of Delegates, who walked out of a meeting as local politicians debated the idea.

"You just don't float a bond issue in Virginia without substantial study and justification," he said.

Although the Virginia Association of Counties has no authority to make law (it is chiefly a lobbying group), the debates here today are likely to be echoed in the state legislature at least for the next two years, officials said.

The stakes in the legislature are high. Each side stands to gain, or lose, millions of dollars in funds that would widen key arteries, build new interchanges or pave dirt roads.

"Transportation is the fragmenting issue," said Fairfax County Executive J. Hamilton Lambert.

The maneuvering got under way formally yesterday in the ornate conference rooms and elegant parlors of The Homestead, a 15,000-acre resort in Virginia's Allegheny Mountains.

There, a succession of politicians, many from Northern Virginia, entreated the association's delegates to support a vaguely worded road bond resolution. The resolution, the result of a subcommittee's compromise reached in the summer, calls on the state legislature to put a road bond up for referendum, but fails to specify how large a bond or, more crucial, who would get the money.

"We object very strongly to not deciding how this money is going to be spent," said Roscoe F. Epperson, a Patrick County supervisor who leads a coalition of rural Virginia counties. He urged that the state road funding formula, which was redrawn early this year by the state legislature to help populous suburban areas, such as Fairfax, be revised again to meet the needs of rural localities.

To Northern Virginia officials, Epperson's remarks were further evidence that the gains made by suburban localities at the 1985 session of the General Assembly will be strongly challenged in the upcoming legislature.

"Our effort will be to keep what we got," said Fairfax transportation director Shiva K. Pant.

Fairfax County Board Chairman John F. Herrity, calling Fairfax "the goose that laid the golden egg," stressed that the county was host to a third of all economic development in the state last year.

Without higher levels of state road funding in Fairfax, he said, Virginia will suffer lost revenues as the county's boom fizzles because of inadequate roads.

Despite Herrity's aggressive speech, Northern Virginia officials acknowledged it is not likely that a state road bond would be up for referendum in 1986, and said they were aiming for 1987.

The association is scheduled to announce its position Tuesday.

Also scheduled for a vote Tuesday is a Fairfax proposal to change the association's voting procedure from the current one-county, one-vote rule to a system based on population. The proposal has drawn the ire of rural counties with fewer than 50,000 residents who would be left with one vote to Fairfax's 13. Fairfax has more than 650,000 residents.

Although the issue is not regarded as critical outside the association, it is another measure of the divergent interests that have distanced Northern Virginia from the downstate jurisdictions that once dominated state politics.

Rural officials lobbied hard this evening to gather votes against the voting shift.

"Fairfax would have more votes than all of Southwest Virginia," said Phill Gay Jr., a supervisor from Prince Edward County who is a leader of the rural coalition. "I don't feel that's fair."