Fairfax County yesterday rezoned one of the last parcels of vacant land along the Capital Beltway -- an action that some said probably doubled the value of the tract's 334 acres to more than $14 milllion.

The decision by the county Board of Supervisors ends years of maneuvering and delays and clears the way for two Canadian firms to develop a large office, housing, and shopping complex on the inner side of the beltway's interchange with Arlington Boulevard (Rte. 50). If all the planned developments occur, the resulting projects would carry a $500 million price tag and add 3.6 million square feet of office space, 1,100 houses and apartments, a 500-room hotel and 100,000 square feet of retail space to the county.

Before yesterday's vote, the land was zoned for housing and was valued at a little more than $7 million, according to county officials. But developers who had wanted to build on the land had agreed to purchase it for more than $14 million -- if the rezoning was approved.

"I'm very pleased," said David S. Weinberg, executive vice president of C. F. Properties (Virginia) Inc., a subsidiary of a Canadian firm that plans to develop the 179 acres located in the southeast quadrant of the interchange. "We hope to have our first buildings completed by 1984."

But Joanne E. Malone, a leader of the neighborhood groups that had fought the rezonings, said, "We're not pleased at all. The supervisors have made a big mistake. What they did was in violation of the master plan."

Existing commercial growth in the area already has spawned traffic headaches for commuters and shoppers, prompting county officials and citizens alike to regard nearby Tysons Corner as a transportation disaster zone.

To win approval of its proposal, C. F. Properties, a subsidiary of the major Canadian developer Cadillac Fairview, and Costain Washington Inc., another Canadian-controlled firm, promised to make $18 million in road improvements, construct lakes to control storm runoff and organize a massive ride-sharing scheme that could put almost 11,000 commuters in no more than 3,300 cars and vans.

If the ride-sharing fails to work as promised, the developers have agreed to limit temporarily the amolunt of office space they would build on the property.

Even if the developers stopped at their proposed limit of 3 million square feet, their project would be a big one -- the equivalent of more than twenty 12-story buildings, and that's not counting a 15-story hotel, 100,000 square feet of retail space and 1,100 houses and apartments. The residential development would be the equivalent of about 2 million square feet. r

Yesterday's move to rezone the land was made by Supervisor Martha V. Pennino (D-Centreville). "What we have before us is the opportunity to do the best possible job for the county and for development of the area . . . ," she said. "If we had an opportunity to do at Tysons Corner what we can do here, we would not be suffering the problems we have at Tysons."

Pennino was backed by six supervisors -- Chairman John F. Herrity, Joseph Alexander (D-Lee), Marie B. Travesky (R-Springfield), Nancy K. Falck (R-Dranesville), Sandra L. Duckworth (D-Mount Vernon) and Audrey Moore (D-Annandale) in the rezoning of the land southest of the interchange. The vote to rezone land northeast of the interchange was the same except for Moore who opposed that change.

Opposing both rezonings were Supervisors James M. Scott (D-Providence), whose district includes the tract, and Thomas M. Davis (R-Mason), many of whose constituents were said to be troubled by the developments.

The rezoned land is part of a 1,300-acre parcel known as the Chiles tract that has already provided sites for Fairfax Hospital, Northern Virginia Mental Health Institute, Yorktowne Shopping Center, Falls Church High School, the American Automobile Association and Mobil Oil Corp.'s marketing headquarters.

It is named for the Earl N. Chiles Sr., a Virginia county merchant who acquired the land in 1924, in exchange for a general store, grist mill and some land in his hometown of Gilmore Mills in the Shenandoah Valley. In the 1930's, Chiles sold the land, but reacquired it when his purchaser failed to make all payments.

The abortive deal turned out very well for Chiles. As Fairfax urbanized, new roads were built. Two of them were Rte. 50 and the Capital Beltway. They intrsected in the middle of Chiles' 1,300 acres, making the land one of the most valuable and sought-after parcels in the county.

Over years, Chiles sold off pieces, but he retained some of the most strategic land. Until yesterday's vote, many of his proposals fell through, as, developers ran up against citizens from nearby subdivisions, who were fearful their neighborhoods would be overwhelmed by the projects that were planned.