Hat and Tails Optional; Jacket Required

So here’s the deal: You invite 320 Very Important People to a fabulous dinner on New Year’s Eve at the White House. Big night, big memories. The men will be dashing in tuxes, the women aswirl in their most glamorous chiffon/beaded/silk/lace designer gowns. Except . . . you’re asking them to spend three hours outside. On Dec. 31. It might be raining. Or snowing. Or just plain freezing.

How to be thoughtful hosts? The White House’s answer: Tell guests to wear silk long johns.

The president and first lady have invited an illustrious list of rich and famous “American Creators”--Muhammad Ali, Robert De Niro, Elizabeth Taylor, Jessye Norman, Neil Simon, Jack Nicholson, Arthur Schlesinger, Itzhak Perlman, Kathleen Battle, Rita Dove, Edward Villella and Mary Tyler Moore, to name but a few--for the White House Millennium Dinner. There will be an elegant meal, late-night dancing and breakfast. Great, huh?

But the invitation also requires accompanying the Clintons to the Mall for “America’s Millennium Gala: A Tribute to the Nation at the Lincoln Memorial.” That’s the outdoor extravaganza produced by Quincy Jones and George Stevens Jr., hosted by Will Smith, with Trisha Yearwood, BeBe Winans, Sam Waterston, Luther Vandross, singers, dancers, an 18-minute Steven Spielberg movie, a speech by the president, and a midnight fireworks and light show.

Did we mention it was a three-hour show? Outside?

“Steven, Quincy and I stood on the steps of the Lincoln Memorial in March and felt that for this historic occasion, this was the place,” says Stevens. “We knew it was going to be difficult, but we’re only going to do it once.”

Stevens believes the dinner guests are quite capable of . . . well, weathering whatever weather.

“These ‘creators’ are noted for their pioneering spirit, so we think they’re up to this,” he says cheerfully. “These people, people of great accomplishment, do not have weak knees. But it will require a certain hardiness, let me put it that way.”

The Millennium Dinner will look, in most respects, like a large state dinner. The 320 guests--celebrities, Cabinet members, congressional leaders and friends of the Clintons--will go through a receiving line and dine inside the White House.

But no state dinner guests venture outdoors in winter. This night, however, everyone will be bused to the Mall at 9:30, except for those with health concerns. “If they don’t want to leave the White House, we have made sure there is a space here for them,” says White House social secretary Capricia Marshall.

The wild card is the weather. “The last thing I heard was foggy and 40s,” she said.

Forties would be great, considering that about 3,000 invited guests--the White House guests plus members from the diplomatic corps, Congress and local elected officials--will be seated in open-air chairs and bleachers in front of the Lincoln Memorial. Heated tents were out of the question, because Hillary Clinton wanted this event to be open to the public--sitting on blankets or standing--and tents would obstruct views.

Guests will receive goody bags with mufflers, hand-warmers and seat cushions, and warm air will be piped under the seats. “We’re also planning on having heated hospitality centers that will be up and down the Mall,” says Marshall. “We’ve taken over every generator on the entire East Coast.”

“I guess I’m going to take my portable thermonuclear heating device, which will be hidden somewhere on my person,” says Michael Saylor, president of Micro-Strategy, a guest who probably could afford a full-body personal heating system.

The White House decided on black tie instead of white tie, so women could wear evening pants. Guests are advised to bring cold-weather gear like heavy coats, hats and sweaters. “Layering is important,” says Marshall. “We’re telling our coat check to be prepared for very large bundles.” There’s even extra time in the evening’s schedule for guests to dive into the elegant White House bathrooms and slip on winter underwear.

Carolyn Peachey, who is coordinating seating, has also turned into an informal wardrobe consultant.

“For women, we’ve been recommending that they get that silk ski underwear, which is very thin so it’s not bulky under a black-tie outfit,” she says. “I’m suggesting it would probably be a wise thing to pick a black-tie pants outfit as opposed to a dress. Obviously, some people aren’t going to be willing to do that, but that’s our suggestion.”

The sweet part, she says, is that most female guests are more concerned with protocol than warmth--they want to make sure pants would be appropriate for the White House dinner. “Would that be all right with Mrs. Clinton?” they ask.

Peachey is telling them to forget formalities and go for comfort. “You should dispense with the black tie and wear what you would wear in a snowstorm. Wear a down parka, wool hat, warm gloves. . . . If someone wears evening sandals, that would be a very unhappy person.”

None of the guests has objected to the trip to the Mall. “Not one person,” she says. “An invitation from the president and first lady is taken with great seriousness and great respect, as it should be.”

Besides, it’s not going to be cold. Really. Honest.

“I have to tell you: I am a determined optimist,” says Peachey, “and I am quite certain that it is not going to be freezing.”

No one else is making predictions.

“Carolyn’s in charge of warmth,” says Stevens. “I’m in charge of joy.”