It was an evening of Virginia politics, suburban gentry style, at the Mount Vernon mansion of Treasury Secretary Donald T. Regan last night.

Two hundred fifty of the Mount Vernon area Republican faithful, each of whom had dutifully pinned on elephant-shaped name tags, turned up to raise funds for Virginia Attorney General Marshall Coleman's gubernatorial campaign. They heard the candidate receive the enthusiastic blessing of the Regan administration, straight from the Treasury secretary's mouth.

"People have been asking me, why did we open our home to you tonight?" Regan told the crowd. "We like Marshall Coleman. We need Republican governors. Your commonwealth -- no, our commonwealth," Regan corrected himself, "needs Marshall Coleman." Coleman took the microphone next, and couldn't have agreed more.

It was Regan's second public campaign pitch for Coleman. Asked later if there would be more campaign appearances to come, Regan said that while Coleman "would like there to be, it will have to be as time permits."

The sponsor of the fund-raising event, the Martha Washington Council of Republican Women, had adorned each pillar in front of the Regan home with the blue posters featuring Coleman's campaign smile. But the real show was out back, where the spacious Regan lawn slopes down to the Potomac, and where Coleman and his running mate, Cirginia State Sen. Nathan Miller, could be seen working the crowd.

Miller, running for lieutenant governor, has ben under fire in recent weeks over disclosures that he had received at least $250,000 in legal fees from the state's electric cooperatives while drafting and voting for legislation that gave his law clients $13.2 million in tax breaks and business advantages.

But last night, standing under a striped lawn tent, the senator was taking things in stride, and even informing guests of a poll that he says shows his name recognition to be 10 percent higher than his opponent's.

"My opponents would like to keep the issue alive, that's for sure," Miller said of the utilities furor. "But generally, I think most people realize what a co-op is, and that I didn't benefit from that legislation, the people did."

Nary a discouraging word about the Miller affair could be heard among the partygoers, who gathered in clumps along the wide lawn, listening to the politicians, the sound of the river, and the hissing and zapping of several bug lamps.