The Fairfax County Board of Supervisors has authorized the county to take responsibility for major repairs and replacement of privately owned, five-inch sewer lines running to more than 12,000 town houses in 18 subdivisions.

As part of its agreement last week with the Lake Braddock Community Association, the largest of the homeowners groups involved, the Board of Supervisors has appropriated $72,000 to be used this year for repair or replacement of the sewer lines.

Additional money will be set aside annually for an indefinite period, officials said.

In the early 1970s, the county permitted the builders of the 18 subdivisions to install five-inch sewer lines, rather than the standard eight-inch lines, on an experimental basis as a way to reduce housing costs. Because the lines were smaller than the county building code required, officials stipulated that the town house associations had to own and maintain them.

According to Supervisor Audrey Moore (D-Annandale), the five-inch lines were to be installed only in a small section of the Lake Braddock development where town houses were less expensive.

"But the county staff began approving five-inch lines even though the houses were selling at a higher rate," Moore said, and "they allowed 17 other town house developers to put them in." The county stopped approving the smaller lines in the mid-1970s after they were found to be inadequate.

Although there have not been many major problems with the five-inch lines, they tend to become blocked more frequently than the larger lines do.

Under the agreement between the county and the designated homeowners associations, the county will repair or replace the five-inch lines with eight-inch lines if the smaller lines break, said R.J. Gozikowski, director of the office of waste management. If a break occurs in the middle of a line, Gozikowski said, it will be replaced with another five-inch line.

The county will assume ownership of, and be responsible for maintaining, any eight-inch lines that are installed, but the five-inch lines will still be owned and maintained by the town house associations.

"It's not a perfect resolution, but it's as good as we were going to get," said Moore, who has supported the transfer of ownership for more than 10 years. The board's decision was unanimous.

Ron Holsopple, the executive director of the Lake Braddock Community Association, said he is pleased with the agreement, even though the homeowners associations are still responsible for the five-inch lines. "We had put aside $27,000 in escrow toward the replacement of the lines. {The agreement} frees up that money for something else," he said.

The 17 other town house developments with some five-inch sewer lines are Oakton Village, The Villages, Keene Mill Woods, Franconia Commons, Bentley Village, The Westerlies, Pinewood Lawns, Terrace Townhouses of Gunston, Terrace Townhouses of Woodlawn, Terrace Townhouses of Annandale, Pinewood Plaza, Reflection Lake, Sequoyah, Reston Section 32 (blocks 2 and 3), Meadows at Newgate, Pinewood Meadows and Brosar Village.