State and national historic preservationists have officially come out against Virginia Power's proposal to install a large overhead transmission line alongside Manassas's historic district.

The historic preservationists and several technical consultants, whose testimony was filed with the State Corporation Commission on Friday, argue that the proposed overhead 230-kilovolt line, which would be installed on 103-foot-high poles along the Norfolk Southern railroad tracks, would mar the aesthetics of Old Town Manassas, driving off future businesses and visitors.

The proposed line should be placed underground, where it would not be visible from Old Town, according to their testimony.

The "result {of the overhead line} would be a tremendous economic pressure to demolish historic buildings and replace them with modern structures suited to other uses," said McDuffie Nichols, of the National Main Street Center, a branch of the National Trust for Historic Preservation.

The commission, which regulates power lines of 150 kilovolts and more, ordered its staff in August to reopen public hearings on the proposed line on Nov. 19. The hearing will be at 10 a.m. at the Prince William Judicial Center.

The order to hear testimony on the proposed line's impact on Old Town and arguments on placing the line underground came at the request of Historic Manassas Inc., a nonprofit organization working for historic preservation and economic development in Old Town. It contended that residents who now oppose the line were unaware of public hearings on the proposal last winter.

The commission had already received a staff recommendation to approve the line, which would stretch 6 1/2 miles from Manassas to an electrical facility near Clifton. It is scheduled for completion in fall 1992.

Under the commission's order, Historic Manassas was required to file all testimony in support of its arguments by last Friday.

Virginia Power, which recently presented alternative proposals for the line's route, must file rebuttals to the testimony by Monday.

Under one of Virginia Power's alternative proposals, the line would be placed on 69- and 67-foot poles one block south of the railroad tracks along Prince William Street. The City Council's utility committee, prompted by concerns over the delays and costs of putting the line underground, recently endorsed that proposal.

Virginia Power officials have said putting the line underground could cost an additional $4.5 million to $5 million and delay completion of the line for a year.

Manassas's electrical consultant told the council last week that to avoid what are called rolling blackouts, Manassas needs a guarantee of additional power from somewhere, either Virginia Power's line or a city-built line, by mid-1992. Last Monday, the council voted to build its own 115-kilovolt line on 80-foot poles along the Prince William Street route if Virginia Power construction is significantly delayed.

According to several technical consultants who testified for Historic Manassas Inc., the line could be placed underground at less cost than Virginia Power has estimated by using different materials. The consultants also testified that the city's electrical demand could be met by turning on the Battery Heights substation, which would feed from the 230-kilovolt line east of the controversial section before the underground work is complete.

Vice Mayor James Payne, chairman of the utility committee, said there would be technical difficulties in using the Battery Heights substation.

"We have engineers and they have told us that it can be done," said Donovan Wine, former president of Historic Manassas Inc. "We want to make sure the city has power, and until someone proves us wrong, we're going on that premise" -- that the city will not suffer inadequate electrical power because of delays in the underground construction.

Historic Manassas has declined to take a position on Virginia Power's Prince William Street proposal. "It {the alternative proposal} just takes away from what we're trying to do," Wine said.

However, Shea Hollifield, of the state Main Street Program, said in her testimony: "Even with modifications, the proposed transmission lines will be intrusive on the historic district and have a serious effect on its overall integrity."