The last time they all got together was in October 1981, before setting off for Anwar Sadat's funeral. This time--the Feb. 28 kickoff of the nonprofit Hyman G. Rickover Foundation--the occasion should be considerably happier.

Only Ronald Reagan will be missing that night from the presidential lineup as Richard Nixon, Gerald Ford and Jimmy Carter pay tribute to retired admiral Rickover. Reagan will be winging his way westward for his California rendezvous with Queen Elizabeth II.

Which may be just as well. The last encounter Reagan and the U.S. Navy's nuclear patriarch had may have been less than joyous. It occurred in the Oval Office shortly after Reagan moved in, and after Rickover's wife told her husband she had heard on television that the administration no longer required his services. The controversial Rickover didn't waste any time getting out. He testified before the Joint Senate and House Economic Committee on Jan. 28, 1981, saying if he had his way he would sink all nuclear-powered ships in the world. The next day he retired.

Since then, he has kept in touch with Nixon, Ford and Carter, dining with each of them when their paths cross. Recently, they've discussed Rickover's nonprofit foundation, which will fund think tanks on trade and energy issues and an education camp for young scholars from around the world. Rickover's relationship with Nixon goes back to the days of Nixon's "kitchen debate" with Nikita Khrushchev. Rickover, acting as Nixon's science adviser on that trip to Russia, wanted to ride in a Soviet nuclear-powered ship so he told the Russian admirals one day that Khrushchev, himself, had okayed it. At sea, the Russians discovered that Khrushchev had granted no such permission but by that time, Rickover had seen what he wanted to.

Though his 83rd birthday comes up Friday, Rickover's pace hasn't slowed. He still travels a lot--in recent months to Israel, Egypt and Lebanon. And he is just back from the People's Republic of China. Meeting with General Secretary of the Chinese Communist Party Hu Yaobong, Rickover observed that his host didn't have all of his teeth.

Keep exercising, counseled Rickover, and he went on to describe his own daily regime of doing 130 toe bends, taking a four-mile walk and drinking 12 glasses of water. "I still have all of my teeth," he said.

Acknowledging that he is missing 16 teeth, Hu, 67, promised to heed Rickover's advice.

Nancy Reagan yesterday quietly checked into John Coleman's newly renovated Ritz-Carlton Hotel in New York City, for which he reportedly spent $25 million in buying and renovation. Her presence there, in a 25th-floor suite overlooking Central Park South, represented more than just a spectacular change of vantage point.

For Mrs. Reagan to take her business away from the prestigious 90-year-old Waldorf Astoria was no small matter. The Waldorf Towers, where she usually stays, is equipped for instantaneous hookup to the White House. The Ritz was not. But Coleman has his own Washington connections as owner of the Ritz-Carlton here, formerly the Fairfax Hotel.

This trip, however, Mrs. Reagan apparently wanted a change of scenery and to be a little closer to the Metropolitan Museum of Art, where she was first guest last night at a dinner and preview of the Vatican art exhibit.

Her husband's deputy chief of staff, Michael K. Deaver, and his wife, Carolyn, recently brought back favorable reports of Coleman's handiwork, which transformed the old Navarro into one of Manhattan's small luxury hotels in a class with the Pierre, the Carlyle and the Sherry Netherland.

Another plus in Mrs. Reagan's hotel guide may have been Coleman's friendship with Joe Canzeri, a Washington public relations consultant who was her chief of staff for a short time last year. He resigned on Feb. 11, 1982, to spare the Reagan administration embarrassment because he had received a favorable home loan and had also double-billed the government for his expenses. Mrs. Reagan still calls Canzeri from time to time to make sure things are well with him. The night he resigned she also called, so distressed that she was in tears as they talked.

Mrs. Reagan will try another New York hotel in a couple of weeks when she returns for the 50th anniversary dinner for Newsweek magazine.

Heads of foreign governments won't get to sleep in the historic Georgetown home of Abraham Lincoln's son at 3014 N St. NW after all. The State Department has backed off from leasing it as a temporary guest house after Georgetown residents let it be known they weren't very happy about all the increased activity the government's high-level visitors would generate.

"We're definitely not taking it," said Chief of Protocol Selwa Roosevelt of the house that was built in 1799, and where Robert Todd Lincoln lived from 1918 until his death in 1926. Real-estate broker Vicki Bagley bought it in 1976.

The search continues for a residence large enough to house not only a head of state but also some of his entourage, while Blair House undergoes the $2 million renovation that could take as long as four years.

Residential areas in Kalorama, Cleveland Park and Spring Valley are considered the most likely locations. The State Department is also looking at houses that the U.S. government owns.

"We don't want to create problems or dispossess anyone, but we would prefer a government-owned house," said a State Department official. "If we had to renovate it, at least we'd be putting money into government property. We just don't want to spend a lot of time on it."

Another consideration is traffic and keeping motorcade distances as short as possible between the three principal destinations: The White House, the Capitol and the State Department.

Meanwhile, with the State Department farming out foreign VIP guests to the leading hotels around town, running the president's guest house has lost some of its glamor. Last week, Juliette Clagett McLennan, who has managed Blair House for almost two years, submitted her resignation. She's agreed to stay on until Protocol Chief Roosevelt can find a successor.

"It's a natural break," said McLennan, "a good time to go on to something else."