The Loudoun County Republican Party continued its streak of gains in local elections this month with the overwhelming victory of H. Roger Zurn Jr. over appointed Democratic incumbent Howard P. Smith in the special election for the Sterling seat on the Board of Supervisors.

Voter turnout for the Nov. 6 general election was 47 percent, a level that exceeded many predictions. Opposition to state initiatives on transportation pledge bonds may have boosted the turnout.

In the past two years, the county GOP has won three House of Delegates contests -- with two of the victories claimed by Linda Rollins -- and the party backed winners in this spring's Leesburg Town Council races.

Meanwhile, Loudoun Democrats continued to battle publicly among themselves as Supervisors Betsey Brown (D-Catoctin) and Thomas S. Dodson (D-Mercer) broke with the board's Democratic leadership over incentives being offered to United Airlines to locate a huge maintenance plant in the county.

Loudoun voters approved bonds to expand the current landfill and authorized parimutuel betting here, but the most lopsided vote was on the ballot issue asking voters whether the chairman of the Board of Supervisors should be elected countywide, as opposed to being chosen by the board members.

Eighty-three percent of those voting said yes, and the change will take effect in November 1991, when an entire board will be elected to four-year terms. The number of districts that will exist at that time is still an open question, however. There are now eight.

More than any single magisterial district race, the contest for Loudoun's first at-large board chairman next year will hinge on the tensions between the increasingly urbanized eastern half of the county and the still-rural west, some political activists say.

"It can be a political kamikaze seat," said Al Sitterson, the chairman of the Democratic Committee. The winner of that race may have to anger either the eastern half of the county or the western half and may have trouble building consensus on the board, Sitterson said.

The draft General Plan for land use would continue to funnel development to the east and preserve open space in the west. Some western Loudoun residents and officials say they are concerned that the intensified concentration of population, jobs, roads and other public facilities will come at the expense of projects they seek in their districts.

That sentiment was a factor in the decision by Brown to criticize two fellow Democrats on the Board of Supervisors, Chairman Betty W. Tatum (Guilford) and Vice Chairman Charles A. Bos (Leesburg), as well as top staff members, for their handling of the talks with United Airlines.

Republicans said the referendum on the at-large chairman and the strong showing by Zurn indicate that the voters are unhappy with the current Loudoun leadership. Democratic chief Sitterson responded, "I don't see any terrible trend," adding that the message may be that "the county doesn't do a good job informing people how their money is spent."

Redistricting will be done before the next Board of Supervisors election, and the primary contests could be as late as September, so many of the elements that will shape the November 1991 county board contests will develop in coming months, political activists say. However, the record of the current board on taxes, spending, land use and many other issues can be expected to be debated strongly, they said.

Loudoun Republican Committee Chairman William Mims attributed Zurn's strong showing to the candidate's hard work, the party's strong organization and "the right issues at the right time." Zurn won 73 percent of the vote.

"It was a disaster," conceded Democrat Smith, who said he plans to become "a citizen community activist." Zurn said he hopes to be sworn in on Monday.

The parimutuel betting initiative does not legalize betting on horses in Loudoun. The Morven Park races or any other organization wanting to run such wagering must first get a license from the Virginia Racing Commission, and the commission has yet to complete its work on regulations for the industry.