Snow fell, lightly at first, and covered the Richard Viguerie home yesterday in McLean, looking like someone was sprinkling powdered sugar over the entire scene.

Horses trotted down the lane with carriages, bringing little girls in Mary Janes, men wearing topcoats and women in Sunday dresses from the parking lot at the church on the corner. Cars lined the street on both sides.

It would have made a perfect Christmas card.

But instead, it was a Christmas party for 300, the second family holiday party given by Viguerie, publisher of Conservative Digest magazine and head of the Viguerie Company, which does political mailing.

"I invited three basic groups: conservatives, people in the government--the administration and Congress--and the media," said Viguerie, who wore a red-plaid vest and a green tie with tiny Santas on it.

Invitations, which were extended by phone and then by Mailgram, explained that the "gestation" period for the party from "conception to birth" was 10 days.

You might have guessed it had taken weeks to organize.

Smiling, helpful people were at every corner of the house. They took the coats and the presents (each guest was asked to bring something suitable for senior citizens in local nursing homes), poured the drinks, served the food, and directed traffic.

About an hour into the party Abraham Lincoln, played by an actor from Gettysburg, Pa. arrived to make the Gettysburg Address. He made his way past the band dressed in Civil War uniforms that was playing upstairs and the Gloriana Carolers that were singing downstairs to the back yard, where a big red tent housed another band, two open bars, a videocassette machine playing "Babes in Toyland" and two tables of food--"Confederate Cuisine" and "Federal Feast."

Babies cried. Adults watched the Redskins game, greeted neighbors and talked about Christmas and politics. Lincoln took the stage.

"I told Mr. Viguerie we ought to get a Ron Reagan, too," said Howard Phillips, president of The Conservative Caucus Inc., when the group he was talking to stopped to watch Lincoln's entrance.

Viguerie stepped on stage to introduce him.

"When Abraham Lincoln arrived I greeted him and said, 'Mr. President, half of our guests are very pleased with the snow and half aren't.' And he said to me, 'Mr. Viguerie, that's how I find most people feel about the country these days.' "

Bob Billings, of the Department of Education, who said he helped start the Moral Majority, didn't have to think twice about how he felt.

"I think the world of President Reagan and I think he is going to run again in 1984, in case that's what you were going to ask me," Billings said, before going on to say he was giving more practical gifts--namely, money -- this Christmas.

Viguerie, whose party seemed to spare no expense, said his Christmas wish contained mostly traditional things.

"For Ronald Reagan and myself I'd wish for peace, freedom for the whole world and to get the economy going again, not only here, but everywhere."