What's a guy in a kilt doing at a black-tie party where they're serving tortillas and enchiladas and the guests are dancing on the stage of Wolf Trap?

"I just feel comfortable in it," said Clark MacGregor, but who was director of the Committee for the Relection of the President (Nixon) back in 1972, when the last thing you wanted to be in Washington was director of the Committee for the Relection of the President. But that was another story.

"This is a MacGregor kilt. My father's from Scotland," he said Saturday night at the Wolf Trap Associates' 10th Anniversary Ball. "I wear it about four or five times a year." Before he pulled out onto the dance floor, he asked the bandleader to play something a little snappier.

"He's worn it six times in the last two weeks," said his wife, Barbara.

"Ask him if he's got on anything underneath," said one guest loudly.

"That's a most closely guarded secret," said MacGregor.

There were few other secrets -- political or otherwise -- floating around Wolf Trap's Filence Center stage, which is spacious and lofty enough to seat 400 (and no more) and leave room for dancing.

Kay Shouse, founder and benefactor of Wolf Trap Farm Park, did have a bit of a secret. Wolf Trap and the New York City Opera are scheduled to produce a show that will open at Wolf Trap and then go to New York next season. "It hasn't been seen for years. And it will be a musical," she said over dinner, smiling. "This is mysterious, isn't it?"

The ball was put on by the Wolf Trap Associates -- not to be confused with the Wolf Trap Foundation, although both, basically, are made up of people who give money to Wolf Trap -- to celebrate the finish of Wolf Trap's 10th season. Guests paid $150 to attend. The "theme was Mexican, hence the looming picture of an Aztec calender hanging from the rafters over the stage, and the painted scene of palm trees in Chichen Itza on the Yucatan Peninsula.

Among the guests wandering around and eating Mexican food -- catered by that non-Mexican caterer, Ridgewell's -- were Gov. John Dalton of Virginia; G. William Miller, Secretary of the Treasury; John L. Moore, president of the Export-Import Bank; Mexican Ambassador Hugo Margain and his wife; Rep. Jack Brooks (D-Tex.), chariman of the House Committee on Government Operations, and Webb Hayes who identified himself as the grandson of Rutherford B. Hayes.

Dalton was fresh from a real political party, the one Sen. John Warner of Virginia and his wife, Elizabeth Taylor, were throwing at their Middleburg farm, Atoka. "Reagan came and gave a pep talk," said Dalton.

Spotting two others from the Atoka party -- former congressman Joel Broy hill and his fiancee -- in the Wolf Trap receiving line, Dalton called out, "I haven't seen you all for two hours."

One another part of the stage, Rep. Brooks sauntered over to Secretary Miller. "No state revenue sharing Brooks practically sang out as he put an arm around Miller's shoulder. "I think it's rotten thievery," Brooks explained to someone else.

But business was soon forgotten when Miller and Brooks, both Texans were introduced to another Texan, a University of Texas alumnus. "We're pushing the Georgians out," quipped Miller with a gleeful laugh.

During his own University of Texas days. Brooks ate a lot of Tex-Mex food and drank a lot of beer, he said last night, reminiscing. "If college is as good now as it was then, I wouldn't have minded staying they forever, he said wistfully.