The world was relatively calm Saturday night, and a good thing, too, because much of official Washington went out to a long, relaxed dinner. Together. At the Alfalfa Club.

The dress: black tie. The guest list: strictly stag and strictly staggering.

"All the top people are here tonight," said one distinguishes soul at the outset of the evening. "If they dropped a bomb in here, we'd alld be in another world."

And all the top people were there, from the president to vice president right on down the line, including Sectretary of State Alexander Haig, current and former Cabinet members, the top brass from the armed services and many, many distinguished members of Congress. Press coverage was restricted, but based on accounts from the revelers, the tribal gathering at the Capital Hilton went like this:

The Very Important Partygoers, more than 600 of them -- Alfalfa Club members, guests and, with luck, club members-to-be -- milled about the reception, glad-handing, sipping drinks and waiting for the president to arrive.

"This is a great night. There hasn't been a president here since Ford," said one guest. "Jimmy Carter never came. Just didn't have the personality for it."

"President Carter was invited every year," said Richard E. Pearson, club secretary. "He just never came. When a president regrets something, you never know exactly why. Ford came, and Nixon, and Johnson, and Kennedy came.We've had both Democrats and Republicans."

The Alfalfa Club, founded in 1913, has gotten together "for longer than any man can remember," said one member, for "good food, good talk, good fellowship. There may be someone who still persists in asking, 'What does the Alfalfa Club do?' The answer is still 'Not much.'"

The club's namesake, "alfalfa," according to an old club program, means "'best folder' in Arabic and other languages." It is also, according to an account from an earlier dinner, a deep-rooted plant "which admits no obstacle in search for moisture."

"The Alfalfa Club," said Rep. John Rhodes (R-Ariz.), the former minority leader and club member, "is a great occasion for good clean fun."

"There's never a serious word said at these things," said Catholic University's Rev. Gilbert Hartke. "It's all quip as quip can."

The club has about 150 members -- the likes of President Reagan, Haig, Henry Kissinger, former secretary of defense Melvin Laird, former secretary of the Treasury Michael Blumenthal, Sen. Howard Baker (R-Tenn.), Sen. Charles Percy (R-Ill.), West Virging Gov. Jay Rockefeller, former attorney general Griffin Bell, Sen. Barry Goldwater (R-Ariz.), Gen. Omar Bradley, Chief Justice Warren Burger, Sen. John Glenn (R-Ohio), Edward Bennett Williams, former CIA director Richard Helms, Ret. Gen. William Westmoreland, Marriott Corp. president J. Willard Marriott Jr., Citibank chairman Walter Wriston and on and on and on.

Saturday night, Haig entered and walked right into Percy, chairman of the foreign relations committee, the committee that gave Alexander Haig a Very Thorough confimation hearing. But former astronaut and Eastern Airlines president Frank Borman was there to referee the encounter. "Hey," grinned Borman, "are you guys friends?" Haig's response was immediate. "Sure we are!" he said.

National Security Adviser Richard Allen walked into and immediately spotted the Mexican ambassador. And what strategic stuff might they have chewed over? Undoubtedly, said one sage standing nearby, "the Mexicans want to know how President Lopez Portilo's gift horse is doing on the Reagan ranch. That was Lopez Portillo's own horse, you know. We gave the Mexicans a gun. Interesting symbolism, don't you think?"

Also spotted around the room: Sen. Henry Jackson (D-Wash.), Lyn Nofziger, special assistant to the president, Redskin right arm Joe Theismann, newsman Roger Mudd, Kennedy Center impresario Roger Stevens, Chief of Naval Operations Thomas Hayward. Everybody was a somebody, so gawking was minimal, except for when the president arrived.

And arive he did, with Kissinger (Alfalfa Club president) and John Glenn (immediate past president) running alongside. He bounded up the red-carpeted stairs with a phalanx of Secret Service men, past the public gathered in the lobby. The Marine band tootled all sorts of patriotic songs, the president smiled, and for a moment or two it was Inauguration Day all over again. "Hi, said the president as he walked by.

After the Marine band played, and the lobster and filet mignon had been consumed, the president rose and spoke, briefly, thanking all for their warm reception and saying that he was very comfortable in Washington. He was received warmly, very warmly. "Gee, he's got a great delivery," said a guest.

The vice president did not speak. And then it was time for the real business of the evening. Club business.

Glenn did a lengthy and well-appreciated monologue of chides and quips ("all sorts of insider things," said one who should know) and Percy got up and nominated his son-in-law, Jay Rockefeller, as the club's annual candidate for president of the United States. Past candidates include Richard Nixon (1964) and Bob Hope (1967).

Club president Kissinger spoke, too, getting further comic mileage out of his famed egocentricity. "My recent trip to the Far East was anonymous," said Henry the K. "I didn't use my middle initial."