The Virginia highway commmission has eliminated the controversial Thoroughfare Gap interchange on Interstate Rte. 66 in Fauquier County, thus deciding one of the bitterest fights in the county's recent history in favor of foes of rapid development.

The interchange, near the Prince William County line, would have cost $650,000 to link the interstate highway with Virginia Rte. 55.

The highway commission's decision clears the way for work to start on the last piece of I-66 between the Capital Beltway and I-81 near Front Royal. Work has also started on part of I-66 inside the Beltway.

The commission said it acted in reaction to "the sentiment of the great majority of citizens" at a public hearing last month to reconsider the interchange.

In explaining its decision, the commission also noted that interchanges are under construction at Virginia Rte. 245, 3.5 miles west of the rejected gap interchange, and at U.S. 15, 5.2 miles east of the deleted interchange.

The Thoroughfare Gap interchange, one of six planned in Fauquier, had been supported by the county Board of Supervisors until July, when the Board voted 3 to 1 to ask that it be climinated. The highway commission then schedled the public hearing that led to the Thursday action.

Opponents of the interchange had contended that it would open the eastern edge of the county to developers and the county's newspaper, the Fauquier Demochat, had editorialized against it, calling it "a most questionable million dollar windfall" for a few large land-owners.

Supervisor Stevenson Mcllvaine, running on an anti-interchange platform, had defeated an incumbent in 1975 who favored its construction. His 1976 motion to delete the interchange was defeated, but a motion to have the county planning commission consider the land-use impact of the interchange was approved.

Last spring, the planning commission voted 4 to 1 to ask the Board to "consider" eliminating the interchange. Planning Commission chairman Philip Nelson. the lone dissenter, argued that this did not constitute a recommendation to delete the interchange, but the other four members wrote a letter to the Board saying that deletion had been their intent.

The county Board then voted to ask the highway department to eliminate the Thoroughfare Gap interchange.

Nelson, who heads the county's largest savings and loan institution, also wrote a letter to the state highway commission on planning commissiion stationery arguing that the interchange should be built.

That resulted in spated of claims of conflict of interest and improper conduct and unsuccessful attempts to force Nelson to resign.

John T. Hazel, a prominent Fairfax zoning lawyer whose family owns about 2,500 acres near the interchange, described the interchange dispute "as the emotional issue of the summer in Fauquier County." Hazel, an ardent suppporter of the interchange, said he personally would take no action to try to reverse the highway commission decision.

McIlvaine said yesterday that the action "gives us a little more breathing space on growth pressure. It won't save us but it will give us a little more time get our planning and zoning work in order."