EVERY CHRISTMAS the rumor about the White House eggnog surfaces again. According to the story -- from the usual reliable, but anonymous, sources -- John Ficklin, the White House maitre d' for 36 years, saves eggnog from one year to the next and uses it as "mother of nog," adding the old to the new batch.

As is customary in these rumors that shake the fate of the nation, Ficklin issued a denial: He said he never mixes the old with the new. But confronted with clear evidence that several independent sources had seen left-over eggnog in the White House refrigerator, Ficklin admitted, "I do keep whatever is left from the Christmas parties, say about four or five gallons -- we don't have room for much. And I serve the old batch to the small, select parties early in the season. Last year, I served it to the press at the unveiling of the Christmas tree in the Blue Room."

The leak in the state secret is that this infusion is what gives the White House eggnog its remarkable power. As evidence, there is the fact that after the libation was served last year in the Blue Room, nothing but effusive praise for the decorations' rare and exquisite qualities appeared in the media. Not one question was asked about how much federal money was spent on the tree.

"It tastes so much better for sitting that year, so smooth and mellow," Ficklin said. "We keep it in the refrigerator, all sealed up. Nothing's going to go bad -- after all, liquor stores keep milk and liquor mixtures on the shelf for a long time. I try to make the new batch at least a week before I expect to serve it. It would be better if we made it in October for December. I like to make it once for the whole season."

The Washington Post is now able, for the first time, to reveal Ficklin's recipe. Even without aging, the recipe's secret ingredients clearly are strong enough to change Republicans into Democrats and vice versa. Ficklin uses a gallon and a half of bourbon, a gallon of brandy and a gallon of rum to 10 gallons of commercial eggnog mix. He serves it with a quart of eggnog ice cream for each punchbowl to make it richer and keep it cold, and tops it all with nutmeg.

In a rare interview, Ficklin told the history of the precious nectar. "We started making the eggnog during the John F. Kennedy administration," he said. "Before that, there weren't that many Christmas parties, or if there were, the visitors just got a cookie and a glass of punch. Kennedy was the first one to give the big press parties."

The development of the White House Eggnog recipe has been a bipartisan effort, Ficklin said. "When we first worked it out, we had a lot of tasters until we got it just right. For a while, we used to put in whipped cream, but people complained it was too rich. We found we had a lot more empty glasses when we didn't use egg white or cream. They don't seem to mind the ice cream."

This year, for the first time since he came to the White House 42 years ago (he was named maitre d' six years later), Ficklin won't be making the eggnog. He's been off for nine months or so following an operation on his foot. He threatens to retire in the new year. "Forty-two years is a long time on your feet. The house has been there 140 years longer than I have, so I know it'll get along without me," he said.

This year the eggnog nod will go to Eugene Allen, acting maitre d'. "I know I'll have plenty of people stopping by to taste to see if I'm doing it right," said Allen. Nancy Reagan said she only tasted it when it was served, but approved of it. "Eggnog is a tradition in our house," she said.

Allen pledged to continue Ficklin's long-established make-it-ahead policy. "That year-old eggnog is nice and smooth. But we didn't have any left from last year." Allen remembers the recipe a little differently than Ficklin: He adds a bit of vanilla to taste, topped, of course with ice cream and nutmeg. "But you need to taste it. You might want to change the proportions. I figure it 4 to 1."

Ficklin and Allen say they serve so much eggnog during the season that they aren't enthusiastic about making it at home. "I'm not a drinking man," said Allen.

Here's a smaller version for smaller houses. WHITE HOUSE EGGNOG (30 servings) 1 gallon commercial eggnog mix 2 1/2 cups bourbon 1 2/3 cup rum 1 2/3 cup brandy 1 quart eggnog or vanilla ice cream, optional Vanilla and nutmeg to taste

Mix eggnog, bourbon, rum and brandy. Pour over ice cream if desired. Add vanilla to taste, if desired and sprinkle top with nutmeg.