The outcome of tonight's party at the Park Lane Hotel in Piccadilly is that Anatoly Karpov will play white Monday in the first game of his world chess championship match with Gary Kasparov.

This gives the former champion and current challenger a small advantage and may slightly change the odds being offered by London bookies, which were 6-4 against Karpov a few days ago.

But getting to the choice of colors was more than half the fun in a ceremony that involved the participation of Prime Minister Margaret Thatcher, a half-dozen trumpeters from the Coldstream Guards, playwright Tim Rice (whose musical "Chess" is the hottest show in London) and about 400 guests, clad in black and white, who sipped champagne and nibbled caviar, smoked salmon and asparagus tips on a ballroom floor decorated to look like a giant chess board.

When the speechmaking began, the party sounded like a session of Parliament, with cries of "Hear, hear!" popping up from the audience whenever a reference was made to English-Russian cooperation. The buffet table's centerpiece was a chess board made of red and black squares of caviar. Drinks, which were served abundantly, included English gin and Russian vodka. But when the time came to toast the game of chess and the spirit of international good will, the guests were given glasses of quite strong Irish coffee with small, dark squares of chocolate embedded in the thick cream at the top. Karpov, the 35-year-old challenger, and Kasparov, the 23-year-old champion, both sipped lightly from the cream without touching the Irish whiskey underneath.

Thatcher's presence was felt long before she arrived, in the low-key but efficient security measures. Outside the hotel, where the red flag of the Soviet Union flew next to the Union Jack, bobbies could be seen checking parked cars for bombs. At the entrance to the ballroom, security officers politely but thoroughly checked guests' invitations -- making some very distinguished foreign chess players wait until they had been cleared -- and advised people to "keep that the invitation about you through the evening."

But inside, beyond the checkpoints, the atmosphere was informal and relaxed. Thatcher, wearing a white scarf thematically decorated with black squares, shook every hand within reach, including one or two possible KGB agents. When she reached Kasparov, they shook hands like a pair of media pros, smiling not at one another but at the flashbulb-popping cameras.

Before introducing the champion and challenger, Thatcher congratulated herself (quite accurately) on being the prime minister of "the fastest-improving chess nation" and confessed that she does not play the game. "I'm told I must not call it a game but an intellectual exercise," she said. When she enumerated the qualities of a good chess player, someone from the audience (which included several Tory members of Parliament) interrupted with a shout of "You've got it all," and she laughed. "We, too, make several moves a day," she said. "We, too, try to guess what moves our opponents will make. The difference is, your games are limited in time. We deal with unfinished history."

The drawing for color was made, first by Kasparov and then by Karpov, from two miniature castles (representing the Tower of London and St. Basil's Basilica in Red Square) located at the corners of the chessboard-floor -- where the castles normally stand at the beginning of a game. The envelope drawn by Kasparov from the "Tower of London" said that his opponent should choose a second envelope from the two inside "St. Basil's." When he learned that he had picked the one that gives him the white pieces, Karpov broke into a smile.

Among those enjoying the ceremony was Tim Rice, joined by several members of the cast "Chess," which will open its American run in Washington next year. Asked whether he plays chess, Rice said, "Not really -- just a little. But I have a chess computer now." He said he was interested in the characters of players at the championship level and the atmosphere that surrounds them. The opening ceremony, with Thatcher, the chessboard motif and the Coldstream Guards, reminded him of his show. "They're both show business."

This particular extravaganza might be considered an episode in the "battle of the banks" for identification with the explosively developing chess life of England. A major underwriter of the match is Save and Prosper Group Ltd., which deals with the general public, offering personal loans, retirement accounts, investment funds and other services. It also has offered a prize of $15,000 (10,000 pounds) to the winner of the most brilliant game played in the match. But the sponsor of the posh opening ceremonies was Duncan Lawrie Ltd., a private bank active in the management of large estates and international banking.

Other English banks sponsoring chess activities include Lloyds, which subsidizes tournaments and special awards that have helped English players to ease into the top-level international chess scene, and Kleinwort Grieverson, which finances the British championship -- an event that begins in Southampton simultaneously with the world championship in London. If England produces a serious challenger for the world championship in the next 10 years -- an often-stated goal of British chess officials -- it will be partly because of the sponsorship given by these capitalists to challengers of the socialized chess system of the Soviet Union.