Lingering in the twilight of transition, the First Lady of the Land called down to her aide, commanding, "Let there be snow."

So it came to pass on the first day of winter, when the sun shone bright and the wind whipped chill, that thoughts turned from landslides to snowdrifts, and about 50 White House staffers and their families got to romp in the man-made flakes that Rosalynn Carter had ordered.

While they built "snowpersons" and slid down two gentle hills on the south lawn of the White House, a bright-eyed tourist stood and wached from outside the great iron fence, wondering why it was so.

"Why is it, daddy," said the young son of a taxpayer from Arlington, "that the president can have snow when we can't?"

The leaves rustled, a squirrel lay dead by a Red Maple, and "This Is My Country," prerecorded and brassy, boomed and tinkled to the masses from so many little gray boxes lining the perimeter of the lawn. "That's a good question," said the taxpayer. "When you're president, I guess, you can have anything you want."

Well, at least he can have snow.

Forgetting the lame-duck presidency for a while -- and their work on President Carter's last budget -- the staffers and their families enjoyed the privilege of power for one of the last times yesterday, at a party so private that even the press was slighted. The guest list, said a press spokeswoman Pat Bario, "could not be divulged."

Yesterday's party, Bario said, was only a prelude to grander festivities today. Beginning at 2 p.m., some 4,000 Secret Service and military personnel and White House staffers will gather on the snow for one last morsel of Southern hospitality, Washington style: hot dogs, cocoa, hot cider, egg nog and Peggy Fleming, skating in a specially built rink under a green and white striped tent just beyond the Rose Garden.

It could not be learned where the snow machines came from, nor how much it cost to get the snowballs rolling. The first lady's spokeswoman, Mary Finch Hoyt, could not be reached for comment.

"She's probably out back playing in the snow," said a White House telephone operator.