One Saturday during the last 100 days, Walter Washington, civilian, bounded into a luncheon at the Capital Yacht Club, his lighter-by-20-pounds frame decked in a three-piece suit by Pierre Cardin.

"Look," Washington said jovially to one friend. "I'm beginning to be somebody. When you deal in the corporate world, you should see how much money goes across the table; you see a different power."

The rapid rate of monetary exchange in the corporate board rooms, especially compared to the way a municipal budget is squeezed dry, seemed to excite him. He opened the jacket of his suit.

"Look, they even have extra pockets for this type of dealing."

The tongue-in-cheek reference aside, Washington seemed sincerely smitten by his new world. The friend kissed him.

For Walter Edward Washington, the 63-year-old native of Dawson, Ga., the attorney and housing specialist who rose from supervisor of the city's public housing authority to become the first appointed and first elected mayor of the nation's capital, 11 years of being the first citizen are over. Often, when the cloak of power is taken from a public official, stories of depression abound. In some stories the journey from the spotlight to life-sans-title detours onto the skids, friends diasppear and the invitations dwindle.

In the case of Walter Washington, according to his friends, tomorrow's milestone of 100 days since he left office marks a time of rejuvenation. "It's upbeat, really upbeat," says Washington, his gravelly voice filed into a buoyant, shrill tone by years of public speaking. "If I had any regrets, they were over in 48 hours. Everyone is disappointed if you lose. I put energy, love and blood in the city. But I'm fine. In fact, I'm having a lot of fun."

The Washingtons have not disappeared. But the police security outside their home in LeDetroit Park has, along with the middle-of-the-night crisis calls and the official Mercury sedan with the trunkful of electronic equipment. From the world where doors are held open and entrances are accompanied by applause and standing ovations, only one perk remains, a license plate that announces. "The First Elected Mayor."

And, of course, the pressures have done a disappearing act. "It's kind of peculiar but you become accustomed to the lack of pressures very early," says Washington. Since Feb. 15, Washington has been a partner with a New York law firm, his office ironically situated in a midtown building where he once banished the D.C. Bicentennial office. Bennetta Washington, a veteran, high-ranking employment specialist with the Department of Labor has not changed jobs. But she has also shown a marked relaxation as the duties of the first lady of the city were passed on.

When the Washingtons attended a private Twelfth Night party four days after Marion Barryhs inaugural, Benetta Washington was wearing a jersey pants outfit. In the past, she rarely wore pants and then usually covered them with a flowing tunic. A number of her friends teased: "You're letting it all hang out." And, obviously one civic dinner recently, she received a citation and remarked almost coquettishly on the flipflop of the spotlight, while her husband sat in the audience waiting for her.

Right now, the adjustments of Walter Washington have drawn public attention. People are startled to see him behind the wheel of a car, a spanking new Chrysler LeBaron. And Washington, driving for the first time in 15 years, had a few trying days of adjustment. "Well, Blair Lee said driving was one of the adjustment factors." laughed Washington. He had been warned not to wave at passers-by but no one had warned him about the no left-turns and such. "So I went into that kind of easy. I didn't want to be a hazard on the streets."

A few encounters with Washington have left people with the feeling he yearns for the old attention. He indicated this himself on Jan. 2, as Marion Barry stood by while Washington had a last chance at the podium. As all the local networks carried the scene live, Washington barked at a news photographer who was bobbing up in front of his face, "Sit down, this is one of my last acts." And a few weeks ago, Washington was standing in line at a drugstore, paying for his toiletries, when he spotted an old friend who was a reporter. Washington talked at length of his new life and reminisced about news stories of the late 1960s.

Even in his moments of wistfulness, the review of past events lacks bitterness and is matched by a determination to have an impact in new directions. Besides the legal work , Washington has joined a couple of local corporate boards, has pitched into the full-voting-representation drive and is preparing an outline of his memoirs. "I will concentrate on the last dozen years or so because I think they were some of the exciting ones for the city," says Washington. He is searching for a publisher but is turning down speaking engagements. (I had to talk myself out of some, cordially, of course. I didn't want to get back into a 24-hour-a-day situation."

In the social settings where politics inevitably mix with fun, he has been slightly boastful of his liberaion.

The night "The Wiz" opened at the National Theater, Washingon approached one of Barry's key aides, James O. Gibson. "How are things going?" he asked cordially. Gibson replied that the work was hard and never ending. Washington had a good laugh, then said, "I told you all there was a lot to do, but no one would believe me. Now people come up to me and say, 'How's the snow removal?" And I say, 'What snow?'" CAPTION: Picture, Walter Washington; by Harry Naltchayan