Adelard L. Brault is a Virginia state senator who represents Fairfax County. He also is a lawyer who in private practice represents one of the companies seeking the county's lucrative cable television franchise.

As state senator in February he voted for a bill designed to exempt cable television companies in the state from the 4 percent sales tax for the massive capital expenditures for cable lines, signal towers and other transmission equipment.

The measure has been signed into law by Gov. John N. Dalton, a cable industry spokesman said yesterday.

The windfall saving to Fairfax Tele-communications Inc., represented by Brault the lawyer, could be more than a million dollars.

"I would have been well advised not to vote," Brault said yesterday. But he said he doesn't recall the measure and strongely doubts he was aware of its beneficial effects on the cable TV industry when he voted for it.

The sales tax exemption measure, one of 2,000 bills the General Assembly considered during its 60-day session this winter, was lumped together with 33 other bills thought to be non-controversial. The bloc of bills moved through the Senate Feb. 28, 10 days before adjournment under a procedure adopted routinely to clear a backlog of business.

Brault -- and all 39 other members of the Senate -- voted for the bills. In the House of Delegates, there was a light opposition, but the bills passed 83 to 5.

But Brault found little sympathy yesterday from two members of the Fairfax County Board of Supervisors who criticized his vote.

"He was ill advised to do, it," said Supervisor Audrey Moore (D-Annandale).

"The perception isn't good," said Supervisor Martha V. Pennino (D-Centreville), adding that she was "dumbfounded that the legislature would give a tax break to the profitable cable industry. "Everything I read says [cable] is a gold mine," she said.

According to the state attorney general's office, Brault's vote didn't violate Virginia's conflict-of-interest laws, which do not address the issue of a lawyer-legislator voting on a bill that would benefit a client.

But Brault noted that the Senate's own conflict-of-interest rules say that senators "shall" not vote for bills when they have "an immediate, private or personal interest in the results."

"This certainly benefits my client," Brault said of the cable bill.

If a hotly contested issue were involved, such as the Equal Rights Amendment, he said, "there would be no excuse for this kind of slip-up. But this thing is easy to happen."

Virginia's conflict-of-interest laws for legislators are weak and riddled with loopholes compared to many other states, according to a recent study conducted by the Virginian-Pilot newspaper. Most states either have set up independent ethics commissions or legislative committees designated to handle complaints of legislative misconduct, according to the newspaper. Virginia has done neither.

"It's a matter of every senator's personal conscience," Brault said. "Nobody checks to seek whether or not" senators follow the Senate's regulations.

In Fairfax, the hotly contested cable issue already has prompted Pennino, Moore and other supervisors to express concern about possible conflicts of interest and possible political pressure in the board of supervisor's decisions on the award of cable franchises.

Brault, the dean of the Fairfax legislative delegation and a former majority leader of the state Senate, is one of at least 13 former or current public officials affiliated with the 19 or so companies that have expressed interest in operating the cable system in growing, affluent Fairfax. Earlier this week, the supervisors approved legislation carving the county into three separate cable television franchise areas that are expected to begin operation by mid-1982.

Industry experts estimate it will cost betwen $30 and $60 million to construct the Fairfax system. If the company Brault represents gets the contract for the entire Fairfax system, the sales tax savings could be over one million dollars.

The exemption for cable equipment is one of many already permitted under the state sales tax law.

Already exempted are manufacturing equipment that produces goods sold in the state, prescription drugs, school lunches, government flags, newspaper vending machine sales and transmission equipment for commercial television and radio stations.

George Douglas, executive secretary of the Virginia Cable Television Association, said the reason the cable industry asked for the sales tax exemption, "besides the obvious, is because the broadcasters had the same exemption for a number of years."

Douglas said his organization estimates that the state will lose about $300,000 in annual sales tax revenue but that once the systems are built in the next few years the revenue loss will "drop off drastically." He noted that cable television increases local public service programming and pays a franchise tax to localities.

Last year the sales tax brought in $534 million in revenue.

The bill's sponsor, Del. Theodore V. Morrison Jr. (D-Newport News), said he proposed the bill after a cable executive from his district told him commercial broadcasting already had a similar exemption. He said a cable industry lobbyist helped him draft the bill.

"It's just a matter of equity," Morrison said of the bill.

Del. Warren G. Stambaugh (D-Arlington) said he is concerned about the growing number of exemptions from the sales tax. "There's very little rhyme or reason for most of the exemptions," Stambaugh said. "They're basically in there because somebody came in and made a good pitch." Stambaugh said he voted for the cable sales tax exemption because there already was one for commercial broadcasting.