It's Friday night, a formal dinner-dance in anticipation of the Mardi Gras ball has just ended, and Chalin Perez holds a private party in his Washington Hilton suite. He is president of Plaquemines Parish, La., a title comparable to county supervisor, and the son of judge Leander Perez. As his father did, he rules the parish like a feudal lord.

David Treen, Louisiana's first Republican governor in 100 years, is among the guests. Perez asks an oyster shucker to escort a newcomer through the party, making sure he tastes all the native food -- the raw oysters and snails, alligator sausage and duck pa te'. The guest complies, then after a few minutes thanks the shucker. "Oh, no, that's all right," the oysterman says, not about to abandon his obligation. "Mr. Perez told me to take you around."

Between Thursday afternoon and yesterday morning, the Washington Hilton was crammed with more than 3,500 Louisianians, kicking up their heels and ambushing the Nation's Capital. Once a year, as they've done for the past 35 years, they migrate from the Mississippi to show the Potomac a thing or two.

It's Mardi Gras in Washington: an abbreviated, sophisticated version of the real thing down South, the brainchild of Sen. Russell B. Long (D-La.), who knew a brilliant way to promote Louisiana industry when he saw one. It's jambalaya, crawfish pie, fillet, gumbo . . . and lots of natural gas and oil.

It's a little something extra, lagniappe, a Cajun word that means something free that you don't expect. "Like the 13th doughnut in a baker's dozen," drawled a woman from Baton Rouge. Bob Hunter, a senior lieutenant in the Mystik Krewe of Louisianians, the committee that organizes the Washington Mardi Gras each year, explained it by reciting this verse: Quartee a half nickel red beans, quartee rice/Lagniappe black pepper to make it taste nice.

Mistaken Identities

The famous Olympia Brass Band was flown up from New Orleans at a cost of $10,000. "That was my doing," said Rep. Robert L. Livingston Jr. (R-La.), the chairman of the weekend, who said he didn't know how much the whole bash cost, though it was probably at least $1 million. But the tuba wouldn't fit on the plane. The musicians managed to put the drum in the aisle (against FAA regulations), but Livingston ended up renting a tuba here in Washington.

This year, in addition to the Olympia Brass, every congressman had his own marching band. They included the Raging Cajuns of John Breaux; Russell's Revelers; Sen. J. Bennett Johnston's Bayou Jesters and W. Henson's Moore or Less Marching Band.

"This is wild isn't it?" said Interior Secretary James C. Watt. Carnival emcee Ronnie Cole introduced Watt as the "secretary of energy" and then introduced Secretary of Energy James B. Edwards as the "secretary of the interior." Cole also introduced Supreme Court Justice Sandra Day O'Connor as "Sandra O'Day." During the chaotic parade -- as people shouted "Throw me something, mister!" -- Watt caught so many trinkets that he began throwing beads and doubloons himself.

Sen. Johnston said one of the best times he's had at Mardi Gras was one year when he was dancing as a member of the masked Krewe with his wife, Mary, and she didn't know it was him. "There was a feeling of . . . invisibility," said Johnston. "You know, everyone wants to be invisible sometimes. You're only inhibited by your base inhibitions."

Kings and Queens

"This is my first flush with royalty, I'm afraid," said His Majesty John Joseph Graham. Graham, president and chief executive officer of a private oil and gas exploration company, was appointed by Livingston, with the delegates' approval. Being King of the Mardi Gras ball is an expensive responsibility, and well-connected Cajuns estimated that Graham could have spent anywhere from $25,000 to $75,000 on entertaining his court and buying them jewelry mementos.

Livingston also chose the ball's queen, 21-year-old Linda Jean Randall, a recent graduate of the University of New Orleans, whose family campaigned for the Republican representative from New Orleans.

Randall and Graham looked resplendent Saturday night. Then of course, came the queens of the court and the princesses, selected back home in beauty pageants. One by one, the young women glided into the ballroom, wearing long gowns and tiaras and waving rhinestone wands. The crowd cheered and waved back, looking for the girl from their hometown: the Crawfish Queen from Breaux Bridge, the Catfish Queen from Des Allemands, the Swine Queen from Basile, the Shrimp and Petroleum Queen from Morgan City and so on.

"What's fascinated me the most," said King Graham, "is the diversity and variety Louisiana has in its young womanhood, a great national treasure."

"It's Washington, what can you say?" said Secretary of Commerce Malcolm Baldrige during the weekend's biggest event, the glittery Mardi Gras ball Saturday night. "This party is everything Sen. Long said it would be. He said, 'It's something else.' "