Now comes what can only be described as the "AA" list, an exclusive amalgam of 30 Yanks and Brits who partied it up with the Windsors and the Reagans on the Britannia Friday night after 220 other "A" list guests had gone home.

The Reagans were celebrating their 31st wedding anniversary as guests of Queen Elizabeth II and Prince Philip, and even the president didn't try to hide the fact that he was impressed. "A year from now I'll be calling you for ideas," he told the queen.

Unknown to the select group of Americans, Queen Elizabeth II had no intention of turning in for the night after most of her guests--56 for dinner and 200 more at a reception that followed--left to go home. She and Prince Philip planned a surprise nightcap of champagne and pink frosted anniversary fruitcake for the Reagans and invited the president's senior aides and several Cabinet officers to stick around for the fun.

"I promised her [Nancy] a lot of things 31 years ago," said the president, blowing out the cake's single candle, "but I never thought of this."

Everybody, including the queen and Nancy Reagan--who could be seen from the pier chatting away like a couple of back-fence neighbors--had been watching the Britannia's Royal Marines go through the precision paces of a spectacular military ceremony called Beat Retreat. When it was over, people started to leave.

"I was ready to abandon ship," said Ursula Meese, wife of Presidential Counselor Edwin Meese, when the ceremony was over. Suddenly, she found herself being discreetly ushered away from the gangplank back toward the drawing room.

The ship's crew gave the Reagans an oversized anniversary card with a drawing that featured a British sailor trying to pull a horse on board the Britannia. The saddle was double with the initials "R" on one part and "N" on another.

Entertainment included a solo of "True Love" sung by Mrs. Reagan to her husband, and also a lively piano rendition of "Waltzing Mathilda" (to the delight of the British) by Mrs. Reagan's accompanist, White House Deputy Chief of Staff Michael K. Deaver. Known for his subtle takeovers of keyboards, Deaver established a beachhead on the piano bench before Her Majesty's Royal Marine pianist knew he was under siege.

"These innocents sitting at the piano have no idea they are being moved over and left with one octave at the bottom," said Deaver's wife, Carolyn.

Surrender was graceful, however, and the marine generously gave Deaver his Royal Marine pith helmet to wear for the occasion.

The queen showed off some of her own gifts, given her during her world travels and displayed on the Britannia's wood-paneled walls. When the Reagans finally got to bed in their shipboard stateroom, it was 1 a.m.

The president slept "exceptionally well, but not long enough," Press Secretary Larry Speakes said the next day.

White House Chief of Staff James Baker and his wife, Susan, couldn't stay for the party because she had to catch a plane, but those who could included national security adviser William Clark, Secretary of State George Shultz, Treasury Secretary Donald Regan, Attorney General William French Smith, Defense Secretary Caspar Weinberger, Senate Majority Leader Howard Baker (R-Tenn.), Chief of Protocol Lucky Roosevelt, with their spouses, and Wyoming's Sen. Malcolm Wallop.