It was at Peter and Margaret Jay's Christmas party at the British Embassy a year ago that Jody Powell first learned he was Joe Alsop's cousin.

Alsop had been seated next to Jody's mother at dinner and about halfway through the meal there was a loud shriek from the back of the room where the two were sitting and a roar of laughter. Everyone turned, eager to be let in on the joke. Which, it turned out, was simply that Washington's super doyen of the political-journalistic-social scene had discovered he was "kin" to one of the new Georgians in the White House, who were making a point of not being a part of Washington.

"It's a tremendous joke on Jody," chuckled Alsop. "Not so much on me. Somehow," he mused, "my family always manages to turn up in influential positions. Though this is rather unexpected."

It seems that in a discussion of family backgrounds, June Williamson Powell had allowed as how Jody's grandmother was a Bullich, which would have made Alsop's great grandfather and Jody's great grandmother brother and sister, making Jody Powell and Joe Alsop fourth cousins.

'The Bullochs were a very, very grand Georgia family," said Alsop. "Archibold Bulloch was the first revolutionary governor of Georgia."

At any rate, regardless of the blood relationship with Powell, Alsop like Powell and says, "He's the only one in that crowd I can communicate with. And his wigfe is enchanting, the real giltedged thing from start to finish. And I do like him."

Some feel this was Powell's christening into the Washington scene, a scene that most of the Georgians had been assideuously avoiding since they had arrived in Washington.

"We were extremely cautious, maybe overly so," says Powell today upon reflection.

"We didn't know that we didn't know who people were. And we had had enough of an experience in Atlanta when Carter became the governor. The lesson we learned was that in a new situation you better be damned sure you know who you're getting close to."

It took them a while to watch and listen, says Powell, to learn the players and to understand the political personal relationships outside the professional arena.

Powell says he's doing a lot more of it now, going out to select parties, though Hamilton Jordan still does almost none.

By now it is late evening in Jody Powell's office and the phone has almost completely stopped ringing. The press has all gone home, the president is away and Powell can relax. Soon the Scotch will come out of the corner cabinet and he will do what he likes best -- hang out. The fire in the fireplace is barely crackling and he has even lost interest in poking it.

"I hate to say it," says Powell finally, "but we probably do see the value now, of spending time with people here just to be spending time with them -- more than we did. There's also more time to spend. At first, when people said to us, 'Why don't you people go to parties?' we thought, 'My God! How could anyone with any good conscience go to parties?'"

But then, says Powell, he started observing Henry Kissinger and noticing that he was going out a lot. "You'd see him," says Powell, "at places you'd never expect to see him, like with members of the press."

And it was not lost on Powell that Kissinger was getting enviable press notices.

Powell attributes much of his new understanding of the Washington scene to Robert Strauss. "Strauss,' he says, "is a good guy to have on your side."

"I've been at quite a number of social gatherings with him," says Strauss, "and this goddam fellow is awfully good at night. He has a grace, a charm and a quickness. He's goddam attractive in the office and in the parlor."

"Jody is more experienced and does it better than I do," says Hamilton Jordan. "And he does more of it than any of the rest of us do. He recognizes it is helpful if it is going to be a personal priority of yours. It just isn't mine.

"i'm here," says Jordan with a cocky grin, "bright-eyed and bushytailed every morning while Jody's out late every night being charming on the cocktail circuit."

Hamilton Jordan's attitude is far more common among the Georgians in the White House. Except for the occasional forays into Washington's social and political inner sanctum by Powell, Frank Moore, Griffin Bell and a few others, the Georgians still do stick to themselves.

"I don't think many people in the administration have developed an inclusive, rather than an exclusive, sense," says former White House speechwriter Jim Fallows.

And this feeling once again has come to include the president. There had been a time at the end of 1977 when those in the administration were said to be expanding their horizons. Now, according to many Carter observers, the president is again closing the wagons.

One political appointee, not a Georgian, who has observed them at very close quarters has this to say:

"Jody is hostile and distrustful of Carter's own appointees at a high level. His attitude toward us parallels his attitudes toward the press. They feel they are a small band against a sea of adversaries.

"Jody is obsessed by leaks," says this observer. "They're pulverized by fears of leaks and they believe if you are mentioned favorably in an article it automatically means you are the source."

Powell sees a trend in Washington that makes it "a mark of honor to publicly undercut an issue or policy regardless of whether you know enough to express it or not."

Powell has learned to deal with people he suspects of leaking or being disloyal.

And he has learned about power, a word the Carter people eschewed when they first came to Washington.

"I see a need for it more and more while I'm here than I once did," he says. "I suppose," he says, "that's the fatal first step (to becoming powermad). You do learn sort of while you're here certain things you do have to do. You just can't let people get away with absolute murder."

He will say that people who have been in Washington before, understand power better than most."Their jobs are a little bit different," he says. "I mean the public hasn't had a history of power-mad press secretaries."

If anybody has learned the game, developed an instinctive feel for the play of forces, for how the game works in the Carter administration it is President Carter's press secretary, Jody Powell.

"He has matured from the standpoint of Washington politics," says ABC's Sam Donaldson. "When he first came he didn't understand that Congress was not going to jump through a hoop; he didn't understand how to stroke people."

"The fellow's aged," says his friend Strauss, "not just matured."

"He's sobered," says Hamilton Jordan. "He has a more mature outlook."

Jody Pwell pours himself a Scotchand-water on the rocks. He sists back down at his desk, hunches over in his chair. It is completely quiet now in the White House. The fire in his office has gone out. There is an eerie silence outside on the snow-covered White House lawn. Through the darkened windows you can see the bright lights near the guard box reflect the huge iron gates that close off the average stroller from those barricaded inside. There is no gray in Powell's hair yet, but there are deep circles under his eyes.

He is reflecting on the idea of Potomac Fever. He says he's never caught it. Then he smiles at himself. "I suspect," he says, "one of the signs of having caught it is not knowing. I'm not knocking it you understand.

"It's just that it's true, someday I'll be leaving and I know that. I expect you approach a city differently if you know that, than you would if you expected to be there for the rest of your life. There's got to be a little bit of a psychological difference. I don't have any ambitions to stay here. There's nothing for me to do here after my time is over.... I'll certainly go back to the South and I expect Georgia... It's like when I made the decision about buying my house here... I don't expect my grandchildren to be sitting on my knee in a house on Lowell Street."