Luther J. Derby III thought the answer to his soaring electric bills was blowing in the wind.

But that was before Virginia Electric and Power Co. learned that the 25-year-old contractor was planning to mingle power from a small, electricity-generating windmill with their kilowatts.

The breeze might be free, but, Vepco officials said the power lines that feed his home on Virginia's Northern Neck near Fredericksburg are exclusively theirs.

"I can't figure out why they're (Vepco) going to so much trouble to fight me," says Derby, who charges that the Virginia utility's rules have made it economically impractical to operate a small, wind-powered generator for his home on the banks of the Rappahannock River.

Vepco officials deny Derby's charges. They argue that their rules and regulations, some of which have been altered since Derby first presented his windmill proposal to them last May, are both necessary and fair.

Others, including some Washington-based public interest groups, disagree and have joined Derby and his windmill in the battle. They claim that Vepco's policies are discouraging alternate energy production at the same time and federal government is spending millions each year to encourage it.

"I have concluded that Vepco is in complete violation of federal rules," says John J. Plunkett, a staff economist for the Institute for Local Self-Reliance. He says that the Public Utility Regulatory Policies Act enacted in April of this year, is designated to encourage utilities to cooperate with small, alternate energy producers.

Derby yesterday said he planned to file a petition with the State Corporation Commission which regulates Vepco to challenge the utility's policies concerning windmill operators. Currently there is only one power-generating windmill in Vepco's service area and it is not plugged into Vepco's power system, Derby said.

Derby's supporters regard his fight with Vepco as precedent-setting. As more private companies market wind and solar energy systems which can be plugged directly into existing grids, cooperation from power companies is critical.

"We have over 200 wind systems installed on other utility systems throughout the United States," wrote Edmund Coffin, chairman of Enertech Corporation, the Vermont manufacturer of the wind generator Derby intends to buy, in one of two letters to Vepco officials. "We have . . . resolved the doubts of all but Vepco."

Coffin, whose company has an obvious stake in Derby's case, said that Virginia customers are "momentarily paralyzed" by Vepco regulations. "No major utility in the country has proposed" similar rules, he said.

The most restrictive of those regulatins requires Derby to pay for a separate transformer for his windmill and a second meter to record any windmill-created electricity sent back to Vepco's power grid. He would also be placed on Vepco's experimental "time of usage" rate, which Derby says would be more costly than his current residential rate.

"That's the main source of controversy" says Derby. The experimental program charges customers a monthly rate based on meter readings during peak hours of use. But if his windmill is Idle "one half hour a month" Derby fears his savings are gone. The Vepco rate plan, he says, could add an additional $57 to his bill each month.

Vepco officials admit that possibility, but argue the fee is needed if they are to maintain capacity to supply electricity to Derby's home, and other windmill users, during windless days.

"He is relying on Vepco to be there when he needs us," says a spokesman for Vepco, which was this month dubbed the "most plagued utility in the nation," by Ralph Nader's energy magazine "critical Mass."

Vepco has recently begin a campaign to improve its sagging image. But Derby says it will take more than talk to convince him.

"I don't want to took like I'm picking on Vepco," says Derby, who nonetheless is seeking money to plaster billboards with what he thinks would be an appropriate message:

"Don't let Vepco shoot the breeze."