In a dusty hilltop wheat field overlooking I-66 and nearby Vienna and Fairfax City, local officials last week broke ground for what will become Northern Virginia's most rural subway stop four years hence.

The $17.6 million Vienna station, to be built atop the I-66 median with parking for 2,000 cars and glass-enclosed walkways over the interstate, will extend the subway's Orange Line another nine miles beyond where it now ends at Ballston Station in Arlington. Metro officials estimate the 25-minute subway trip between Vienna and downtown Washington will cut rush-hour commuting times in half for many residents in outlying Northern Virginia communities.

The opening of the Vienna station will add four new stops on the Orange Line -- East Falls Church, West Falls Church, Dunn Loring and Vienna -- and will be the subway system's first real penetration into Fairfax County.

The first station in the county, although just barely, will be the Huntington station south of Alexandria and the Beltway, which will be the end of the Blue Line through Alexandria. It is scheduled to open late next year. The Franconia-Springfield station, the end of the Yellow Line, is expected to open in 1989. Both the Blue and Yellow lines will run through Alexandria, splitting at the King Street Station.

Fairfax City Mayor John Russell, who in 1971 told a Metro hearing he had faith in God and Metro but never expected to see either, promised a crowd of 200 at last Wednesday's groundbreaking that he would eat the 1971 newspaper story that reported his remark the day the Vienna station opens.

Vienna Mayor Charles Robinson called the groundbreaking the second most important event in the history of nearby Vienna -- after the installation of the town's water and sewer system 35 years ago -- and said Vienna residents had mixed feelings about both events. He said people in Vienna are afraid the residential character of the town will change, but "we will do everything we can to preserve" the quiet town.

Robinson noted that 130 years ago Vienna residents hailed the coming of rail to the city, and what later became the Washington & Old Dominion Railroad is now a regional bike trail.

Although called Vienna, the last station on the Orange Line actually is in the middle of several Fairfax County subdivisions, about halfway between Vienna and Fairfax City. The Dunn Loring and West Falls Church stations also are in the county and East Falls Church is in Arlington. Construction of these stations already has begun.