A watchdog group monitoring the construction of Interstate I-66 in Fairfax County decided last night to mount a letter-writing and phone call campaign to combat what the group sees as deliberate insensitivity to their concerns by state highway officials.

The meeting was prompted by news that the Virginia Department of Highways and Transportation is starting to place lights atop the 40-foot-tall walls that line part of the high-speed, limited-access route. "They know that we're opposed to this" because it will shine bright light into nearby neighborhoods and because their siting would supposedly enable the department to widen the highway at a later date, said committee member Vivian Barry.

"That they told us about the lighting plan when it was already a fait accompli just rubs salt in the wounds," she added.

Asserting that the department has broken its written promise to consult with the 10-member group -- a citizens' advisory board to the Fairfax Board of Supervisors -- concerning I-66 lighting, sound barrier and landscaping decisions, members said that they would take their case to Virginia Gov. John N. Dalton, U.S. Sen. John W. Warner, Rep. Frank Wolf and several local politicians.

Members also said they will join forces with the Arlington Citizen's Advisory Council in their attempt to influence the design details of the I-66 extension inside the Capital Beltway, one of the most controversial and fiercely opposed roadways in Virginia.

Committee member Robert Barry said that although the state isn't legally required to respond to the group, "We've got to bring all our political presssure to bear. We have to show our strength."

In addition to the lighting plans, the group sharply criticized the department's plans to erect 12-foot metal walls near McLean Park, at the junction of I-66 and Route 7. "These walls are more ugly than anything you've ever seen," committee member Marty Conlan said.

Highway department officials have consistently maintained that they always act with the welfare of the highway's neighbors in mind. The officials also have complained of what they call eleventh-hour opposition to their efforts.

The 9.7 mile, $170 million I-66 extension is scheduled to open next year, linking the beltway with the Theodore Roosevelt Bridge across the Potomac, and it is supposed to lop off 15 minutes commuting time for many Northern Virginians.

Committtee members last night pledged to reassert their influence in the project, which citizen's groups held off for almost 10 years with law suits before construction got the go ahead in the late 1970s.

"We've been spinning our wheels for almost a year now," Vivian Barry said. "I'm getting pretty tired of turning the other cheek."