Charles Kirbo, senoir adviser to Jimmy Carter, once turned down an appointment to the U.S. Senate and says he does not propose for his feet to get tangled in the White House now.

"What would be the point of me in Washington?" he rhetorically demanded, at a talk in his Atlanta law office.

"The minute you sit down, you become part of it, start thinking the same things everybody else does, start listening to the consensus.

"I think I can be more effective or useful if I'm not up there trying to prove, that what I did yesterday was right."

It is true, however, that the President-elect entrusted Kirbo with the screening and interviewing of vice presidential candidates, and that for more than a decade Kirbo appears to have been the behind-scenes keel. When Carter needed money, Kirbo raised money. When Carter had doubts, Kirbo urged him on.

He has been called Carter's alter-ego, the gray eminence of the president-elect's world view.

As Kirbo tells it, he's plain man of reason able good sense, with no political ambition whatever, wishing merely to practice law in Atlanta to pay of his 110-acre suburban place and large South-Georgia farm, bought with his law-practice income in mind - "more than any government job could pay," as he says.

He is a partner in the firm of King & Spalding, as was Attorney General designate Griffin Bell, a firm which has a "good reputation" in corporation law, according to a well-known corporation lawyer in New York. But Kirbo is a rarity, a trail lawyer in a field where most lawyers almost as soon lose the case as have to go to court with it.

Kirbo-watchers in Senate offices and elsewhere are afreed that Kirbo's trail work has given him the useful knack of sifting from half-truths.

Not surprisingly those traits stood Kirbo in good stead when screening candidates for Vice.

(He once told Bob Strauss, chairman of the Democratic National Committee, that it was a really lousy job, and when Strauss asked why a job of such prestige should be called lousy, Kirbo said, "because it ruins all a fellow's prejudices.")

He had a personal choice - Sen "Scoop" Jackson - in mind originally, but gathered all the information on which Carter based his selection of Fritz Mondale.

"He came on every quiet," said an aide of one of the candidates being considered for Vice President. "By the time he got down of his real business, you knew a few things:

"First, he is a professional. He seemed to have no personal involvement, but a detachment. He was courteous, and I know (the losing senator) thinks highly of him."

Another Senate aide said he began to notice last May that Carter and Kirbo seemed to be on quite separate schedules, and concluded they must get together by phone a lot.

Kirbo said that as a matter of fact during the campaigns Carter feel into the unfortunate habit of phoning him at 6 or 7 in the morning "to see if I was up."

Washington pundits dearly love kitchen cabinets and unseen powers behind thrones and guides and mentors in general, especially if they are somewhat picturesque, as Kirbo certainly is.

"Often he has ignored my advice," Kirbo said, tensing a bit when someone suggested he was well on the way toward being cast as a combination Socrates-St. Francis of Assisi, "And had done quite well without it.

"I do not get my feelings hurt. I have never tried to persuade Jimmy, merely to give him my view. I never designed any relationship with Jimmy, it just sort of evolved.

The relationship that just sort of grew, as Kirbo puts it, began in 1963 when Carter suspected a ballot box had been stuffed against him in a race for the Georgia legislature. He didn't know Kirbo, but somebody recommended him as a lawyer.

Kirbo had no earthly idea how to prove Carter's suspicions about the ballot stuffing, and thought it might well be unprovable, but as usual he began at Go, so to speak, and got a court order impounding the ballots in question.

Somewhat to his surprise, when the box was opened, a whole fistful of ballots, all folded together in one mass, was right there on top. Methodical procedure, rather than brilliant fire works, won the case that time.

Later, when Carter became governor of Georgia, Kirbo was named chairman of the state Democratic Party, a job he did not partcilarly relish, but in which he apparently made extremely few enemies. 'Unsuccessful Farmer'

Kirbo has silvery hair and many turn up in the office wearing a sports jacket and a lot of yellow and brown, looking neat and even natty, though yellow and brown are not standard colors for corporation lawyers generally.

During his chat someone came in to say Carter was going to have a televised news conference and the partners of King & Spalding were gathering in a room to watch it.

Kirbo stood up quickly and lost no time getting to the room. It was learned the conference was not going to be seen on television, after all, and Kirbo was the first to leave, without comment, to return to hi office.

On the way he said, "What I really am is an unsuccessful farmer," and was about to make some pastoral observations-on his Angus cattle when Hughes-Spalding, chairman of the law firm's management committee, broke into uncontrolled laughter.

Spalding had been walking down the same hallway and heard the comment about being a farmer.

"An unsuccessful farmer," Spalding gaspes between spasms. Greatest line he never heard in his life. He got on an elevator and the door shut on him still laughing and still saying, "Oh, an unsuccessful farmer."

Well, I am," said Kirbo with dignity, trusting there would be no more rude laughter when he got back to his own desk.

He says he expects his own role to dimish:

"When I say Jimmy has moves beyond my competence to advise him. I mean that it's one thing to know a little bit about Georgia, as I do, but another thing to know about the nation and the world. The things I do not know about are endless. I have not moved with Jimmy into his new sphere . . ." But as a Carter aide once told a reporter, "If Carter hasn't talked to Kirbo, he hasn't talked to anybody." A Soft Voice

Born in Bainbridge in Southern Goergia 59 years ago and educated at the University of Georgia, he practiced in Albany and, at the urging of Griffin Bell, came to King & Spalding, an Atlanta institution specializing in corporation law, in 1960. He had always had a soft voice, deep, musical, and well articulated by Southern standards.

He is married, the father of three daughters and a son. Family pictures hand on his office walls. The teen-age son is heavily into Country and Western music and has a band which often plays in an outbuilding on the farm, a structure carefully lined with egg cartons in the interest of pastoral quiet.

Asked about his screening process for the Vice President, Kirbo said. "Well, if had not been for the McGovern experience, we would not have known so much.

"It was a heap easier fo us - I started as soon as I saw might win the nomination. I talked to maybe 20 or 30 people about each possible candidate, and I got others to talk to people who one way or another might know about problems we didn't. People like aides, office workers, people in the press, even people who know all the rumors."

Kirbop then submitted candidates to what he hopes was a foot-proof questionnaire requiring tax audits, reports on outside income, medical treatment, etc., in which the only way a man could keep hidden was to tell an outright lie.

Kirbo says his role was only to gather information on which Carter could decide for himself, but it probably did not hurt Mondale's chances when Kirbo said. "I liked him immensely when I talked with him."

Kirbo told a friend, "You know what impressed me most about Mondale? He was the least complicated man I met in Washington, and I thought 'now that man would be easy to get on with."

Kirbo said, "I did not think Mondale was as liberal as his image - a thing that is often true of liberals."

Kirbo has always had a sensitivity to the political dangers of casting the business community as all-out villains and of embracing the everything that roars on wheels had more than common shagginess.

He once stopped a campaign project that would turning shown Carter buzzing about on a motorcycle.

He once warned that so many liberals were turning up at Plains (many of them quite uninvited) and announcing to tne press that they were in line for something or other, that Carter was getting the image of being a haven for only liberals.

When Carter was governor of Georgia, Kirbo's chief anxiety was that Carter was launching too many bills in the legislature on too broad a front - Kirbo thinks an executives cannot do everything and certainly not everything at once, and that more is accomplished by zeroing in and following through than by raising a general up-roar in a different directions at once.

In this sense, at least, Kirbo appears to be (as many have labelled him) "middle of the road."

Carter, as he points out, makes his own decisions, but it may be correct to say that Kirbo could be a restraining influence.

Certainly Kirbo's attention to big contributions in Texas, when personally went there to un-freeze vital primary campaign money for Carter, suggests that he is adept at persuading wealth business interest that Carter is no drawling bogeyman. Southern Sport

Kirbo likes to josh. There is as style of ironic banter in the South that Kirbo is good at, a kind of ribbing, and it is also delightful sports as long as both sides know now to play.

On a certain day Carter said he would announce his choice for Vice President. Kirbo went over early, and said, "I have some bad news to tell you about Mondale," But Carter knew he was horsing around and grinned and said, "It's Mondale."

Carter, knowing Kirbo's way of working, knew anything "bad news" about Mondale would not be coming from Kirbo at the last minute, but early on, Kirbo, knowing Carter, knew he could safely joke about a matter of great national importance, and knew he could joke about a his own responsibility in checking out the vice presidential candidates,

It is a style of banter that works only between intimate friends, and only when each has perfect confidence in the competence, brains and faithfulness of the other. Mules and Peaches

As writer settles in, Kirbo is fixing to prune 12 kinds of good grapes - as well as the others he grows "just for the hell of it." He is frequently "fixing to" do various things when he is not already engaged in "carrying" something somewhere. He does not send things or take them, he carries them or asks someone else to. He does not prepare to do something, he fixes" to do something.

Many believe he does not know what the hell a parameter is.

Kirbo also has the common southern attachment to (if not actual reverence for) the common mule. He has one which he tries to justify on economic grounds.

The novelist Faulkner kept a portrait of a mule in his bedroom. Many southerners of both sexes and races have early memories of the mule, which symbolizes the hard times of the past, and the exultant liberty of the day one is first hoisted onto Old Pompey or Old Paint and is no longer earthbound by one's three-year-old legs. The mule, compared to a horse, stand for intelligence, hardwork, independence, stubbornness, pride and the virture of not being too big for your britchers or too clever by half.

Kirbo, in any case, went to some trouble to acquire a mule.

"Diease is a problem with our peaches here in Georgia," he says, commencing the ancient litany of the farmer and gardener who will always convince you that Iceland or the Mohave is perfect farming country but Gergia is very hard, very hard. "I guess my favorite is the 'Belle of Georgia.' The 'Elberta' is reliable and productive and bright-colored, but no, it dies not have the quality of 'Belle.'"

He has seen the ignorant or careless purchaser pass over "Belle," the great but not very showy peach, for the superficially gorgeous "Elberts," which is astringent tough, fibrous and dry when compared to the melting and nectar-flooded "Belle." There is more to quality and value, in other words, than meets the innocent and inexperienced eye. Nibbling Into Trouble Former Gov. Lester Maddox, who now holds forth at his Pickrick eating establishment and whose views about the general worthlessness of Carter are well known, said of Kirbo that as far as he knew Kirbo is "able and good."

Robert Strauss, who was uneasy once when the rumor went out that Carter would dump him from the Democratic National Committee, said of Kirbo that "Number 1, he is highly intellectual - he tries to conceal it. Number 2, he is exceedingly wise. He has judgement. I don't care how bright they are, let's test them for judgement, because that's all there is. He is not sly, that is the wrong word, but he is very smart. He really is a most attrative man."

I felt sorry for Nixon, hell, he had no luck with his advisers," Kirbo reflected. "Think of the incredible judgement of those tapes. Something you can say in heat, 'we ought to kill that sonofabitch,' but later you say 'no, we should not do that.' Of course Nixon sort of nibbled his way into trouble."

Kirbo thought a bit and when Washingtoncame up again he said, "Well, I've no desire to get into anything that somebody else is doing well. I'm more apt to be there if something is not going well . . .

"I'm awfully glad Jimmy has got Griffin," Kirbo says of his former partner, though Bell's appointment stirred protest over his civil decisions and his memberships, in clubs that exclude blacks and Jews. "I feel better about not being there myself, knowing Griffin is there.

"I do not mean anything against Washington. I know it has an allure. I can see how it would be exciting to be there, to know what is really going on. But you know how it is if you sit down in a Washington office. Hell, you can spend a whole week just out-lining the best way to handle the opening of the mail. You can sit around working out the best damned mail-opening system there is. Meanwhile, the world is going on by."