The departure of Bert Lance from the Carter administration leaves a 6-foot, 4-inch gap in both the top command of the government and the inner circle of Jimmy Carter's friends.

There may have officials with more influence on vital decisions in a wide range of fields than the director of the Office of Management and Budget. But few such individuals come to mind.

And there may have been men with whom the President found it easier to relax and discuss anything from his tennis serve to his transportation policy. But they are hard to name, too.

What is almost beyond refutation is that there is no one in the administaration with Lance's combination of official power and personal friendship with the President.

At least that was the case until the floodgates opened on the cascade of financial manipulations that finally washed him overboard yesterday.

"I don't think there is any way that I could find anyone to replace Bert Lance that would be in my judgment as competent, as strong, as decent and as close to me as a friend and advise, as he has been," Carter said yesterday.

For a time, when the charges against Lance were of uncertain dimensions, Carter kept his distance. The frequent tennis games and informal luncheons disappeared from the presidential schedule, and Lance was, in the words of one OMB colleague, "kind of wondering where he stood."

That question was answered in dramatic fashion on Aug. 18, when the President flew down from Camp David to introduce Lance on national television and proclaim that he enjoys "my complete conndence and support."

That action raised some eyebrows among politicians in both parties, who had a high opinion of the President's political astuteness and who knew that the comptroller of the currency's report on Lance's banking practices, issued earlier that same day, was anything but the complete exoneration the President's action implied.

When a White House aide was asked the next morning why the President had been so eager to link himself to Lance's dubious prospects, he answered in three words:

"Because it's Bert."

During his salad days, when Lance was often called the "deputy President" or the "second most powerful man in government," the OMB director liked to show his humility by insisting he was no special shakes. In June he told The Washington Post, "I'm not conscious of anything where I'm involved in a way that is out of character for the man in my job."

In truth, any budget director enjoys a legal mandate to intervene, on the President's behalf, in the major policy problems and day-to-day decisions of every department of government.

His leverage lies in his position of the apex of the governmnent's budget-making process, a year-round activity that requires scrutiny of the major and minor programs of the vast and variegated bureaucracy.

To that traditional duty, Carter added another assignment for Lance, which increased his power even further. The OMB director was given responsibility for directing the President's promised "bottom-up" reorganization of the executive branch of government.

That process is just beginning, but even in its early phases, Lance was not reluctant to use his power to protect what he took to be the President's goals.

The head of one White House unit that was targeted for sharp reduction in the summer reorganization of the Executive Office staff worked strenuously to avoid the fate. "In the end," said on observer of the struggle, "he just gave up and realized Lance was going to have the last word.

The ability to get "the last word," or at least the most timely visit with the President was the key to Lance's success - while it lasted. Hamilton Jordon, who enjoys such access himself, said Carter "looks on Bert almost as an extension of himself."

And the intimacy of that personal relationship was ultimately both the source of Lance's power and the force that delayed his departure long after most - inside and outside, the White House - considered it inevitable.

The Lance- Carter friendship began in 1966, when Lance was president of the relatively small First National Bank of Calhoun, Ga., and Carter was an obscure state senator, a longshot candidate for the Democratic gubernatorial nomination.

In an interview last spring, Lance recalled that they met during a planning conference in Rome, Ga., where Carter was holding forth under an oak tree.

"I walked up to him standing under that tree and was tremendously impressed by what he was saying and his reasons for wanting to run." Lance said. "I applauded that as a businessman and told him I'd help him."

Carter lost in 1966, but came back to win in 1970, a year in which partial records show $1,500 in contributions from Lance.

The Colhoun banker, five years Carter's junior, had limited political or governmental experience. The son of a small-town college president, he began as a teller in the Calhoun bank at 20, married the bank president's daughter and became president himself in 1963.

His career seemed firmly rooted in the abanking-business worlds, where he operated with a daring that gave him conspicuous success. But as the friendship with Carter ripened, Lance was drawn more and more into the political realm. Ultimately, of course, it was the political unacceptability of some of those buccaneer business tactics that caused his downfall.

The first step into politics was his accepting a bid from Carter to take over the Highway Department, when Carter became governor of Georgia. By every account, Lance was a conspicuous success in that job, reducing the number of employees, increasing activity and eliminating at least some of the more egregious patronage practices.

In his typical fashion, he did not dally much with details once he had installed his own people in the bureau, but instead became Carter's troubleshooter on the reorganization of the entire Georgia governmental structure.

That job involved uncounted hours of negotaition and battling with the legislature, where Lance once again proved singularrly skillful on Carter's behalf.

It was only logical, therefore, that he should become the Carter group's candidate for governor in 1974, when Carter himself was barred from seeking re-election by a (consequently changed) provision of the Georgia constitution.

Lance ran well in the Democratic primary but was hit hard in mid-campaign by charges that he was using his own wealth and borrowings from his bank to finance his campaign.

George Busbee, the legislator who made those charges, narrowly edged Lance to gain a place in the runoff against ex-Gov. Lester Maddox. Busbee won, as many in Georgia feel certain Lance would have, had he been Maddox's runnerup opponent.

With his own political career blocked, at least temporarily, Lance shifted his ambitions back to the banking field and - with the help of some of his now-famous loans - took over the National Bank of Georgia in Atlanta.

He was busy expanding that bank while Carter was conducting his two-year campaign for the presidency. Lance was not conspicuous politically in that period. His and his family's known contributions to Carter totaled only $2200.

His bank did make loans totaling $4.7 million to the Carter family peanut business in Plains to build a new peanut sheller and warehouse and finance crop purchases. But those loans were commercial transactions and have not incurred any criticism.

According to others in the Carter campaign, Lance "had a few small meetings" with businessmen, which may have produced contributions from them to Carter, and occasionally was consulted by the candidate.

But when Carter picked him as his director of OMB, it was less a reward to a valuable political worker than a recognition that Lance's talents would be needed by the new administration in Washington.

As OMB director, Lance exercised notably loose reins, letting his Georgia deputy, James McIntyre ,run senior staff meetings on most occasions, and turning over day-to-day direction of both budget and reorganization projects to two younger associate directors.

But he became a valuble ambassador from the White House to the business from the White House to the business community, which viewed him as the strongest advocate of conservative fiscal policies in the new administration. He developed innumerable friendships on Capitol Hill and in the press corps, and carried the views of congressman and journalists back to his friend in thee White House.

But him impact was felt on such major decisions as the scrapping of the $50 rebate and the continued emphasis on the goal of a balanced budget. And he was seen almost daily in the company of the President, on the tennis court, lunching off trays in the Oval Office or talking as they strolled the White House grounds.

Many have wondered what drew Lance and Carter together. On the surface, they hardly seemed similar personalities, Lance was epitome of the big, bluff, extroverted go-getter, a glad-hander who "never met a man he didn't like." Carter, small, quiet, self-contained, even shy in those early years, had a wary look in those paleblue eyes.

Lance, from his own statements, was a man with a fine disregard for the nagging details of life - like balancing a checkbook or keeping careful records of his loans. Carter is a fuss-budget of formidable proportions, who insists on the most scrupulous attention to detail.

But despite these srong surface differences, others in the Georgia group at the White House and OMB see far more fundamental similarities.

"They are both deeply religious," said a former Atlantan now in a senior administration post, "and they both have a drive for success, for attainment, that is rooted in their sense of religious responsibility."

Lance andhis wife, LaBelle, are Methodist; the Carters, Baptists. But they have worshipped at each other's churches, and both men have given ample testimonly to the central role of religious faith in their lives.

The ambition is equally evident. Lance told Washington Post staff writer Sally Quinn, "I've always tried to set some kind of goal. I wanted to be better than anybody in the banking business . . . I have you think this sounds like a naive statement but all of us have been given a lot. And so a lot is expected in return."

That, many of their colleagues believe, is why Carter was instinctively sympathetic to Lance when the attacks on his financial operations began. And that is why he waited so long - longer than many of his advisers though prudent - to accept the inevitablility of Bert Lance's departure.

"If Bert was not what he seemed," said one student of the Carter administration, "then someone was bound to ask: Is Jimmy?"