Two years ago, when the question of the need for a White House chief of staff first arose, Hamilton Jordan pronounced himself unfit for the role because "I'm not an administrator" and I'm weak on the issues."

Today, as Jordan begins functioning in the job whose necessity President Carter long denied, he says he is still lacking in "substantive policy back-ground on domestic and foreign issues but will try to relieve the president of the burden of resolving conflicts on a broad but undefined range of policy questions.

Jordan said last night that his new assignment "will require me to make changes" in his approach to his job.

"Like anyone else," he said, "I have my strengths and weaknesses. But one of my strength is I know my weaknesses."

The belief among many of his associates is that Jordan will use his enhanced authority with Cabinet members and other White House aides primarily to tune the administration's decision-making to the pitch he thinks most likely to provide Carter a victory in his 1980 reelection bid.

And for that task, they agree, the 34-year-old Jordan is the best man in Carter's employ.

In the first 48 hours since Carter officially designated the manager of his successful gubernatorial and presidential campaigns as his White House chief of staff, Jordan has drawn masses of flak from congressional Democrats, who blame him for firing some of their favorites in the Carter Cabinet. Cartoonists have depicted him as the Lord High Executioner of the White House.

But, inside the administration, there is widespread agreement, first, that the move to discipline the decision-making process was long overdue, and, second, that given the proximity of a difficult presidential campaign, the "politicization" of the administration was inevitable.

But two concerns are being widely, if privately, expressed:

What policies and what people may be thrown overboard as Jordan tries to use the power of the White House to pull Carter off the political sandbar where he is now stuck?

Will the new chief of staff acquire, in his on-the-job training, the administrative skills and policy perspectives he will need to avoid creating serious new problems for his boss?

Jordan has repeatedly insisted that he lacked the "range of ability" to be the chief of staff, even if Carter wanted one, which he never did until last week.

Those who know Jordan and have studied his work confirm his judgment of himself.They differ only in whether they believe or doubts he can grow into the role.

T. Mc.N. Simpson, the University of Tennessee political scientists who has written the most detailed study of Carter's term as governor of Georgia, and who is generally a Carter admirer, said in an interview yesterday:

"Jordan was important in his [gubernatorial] campaign, but not in his administration. He had the title of exectuve assistant, but he was the least administratively oriented of all the people in what Georgia reporters called "the youth corps.' He was poor at running anything. He had no follow-through and he really didn't like to deal with other people."

Referring to a habit of self-isolation that has recurred often in the White House, Simpson said Jordan "hid out in the basement from people he should have met, leaving Carter to deal with them."

Similarly, Nicholas Lemann said of Jordan, in a generally friendly Washington Monthly profile: "Jordan had two specialties -- making instinctive political judgments and drawing up comprehensive plans of battle -- that, along with his closeness to Carter, were his strengths then and remain so today . . . . What Jordan wasn't good at was day-to-day administration. He was know for being impossible to get in touch with, for never being on time, for staying away from the office for days at a time."

Midway in Carter's four-year term as governor, Jordan turned over his top staff job to Frank Moore and busied himself with politics -- acting as deputy to Carter in the 1974 national Democratic campaign and then setting up Carter's presidential bid.

Simpson said his research indicated that Moore, now Carter's congressional liason chief, "though much less bright than Jordan, was much more helpful to Carter as executive secretary."

From the monent he arrived in Washington after Carter's 1976 victory, Jordan has followed the same course: to defend his position as preeminent among Carter's inner circle, but also to avoid assuming responsibility as chief of the Carter staff.

The first (and last) direct challenge to his preeminence came from another young Georgian, Jack Watson, who had spent the campaign period planning Carter's takeover of the government. Watson had come to presume a dominant role for himself in the transition period. Jordan moved swiftly -- obviously with Carter's full support -- to assert his dominance over Watson and his plans.

In those days Jordan's office was receiving hundreds of telephone calls every day. Then, as now, he returned few of them -- often no more than 10, he told an interviewer. He disappeared from his temporary office for hours at a time, and no once could find him.

Shortly before moving into the White House, Jordan told Sally Quinn of The Washington Post that he would not get involved in issues:

"The issues are not my interest. I don't study them. I don't consider myself well-informed on these things. I don't do it well . . . But i'm good to plan the strategy to help push those issues. . . ."

Jordan told Quinn, "i'm a mess . . . i'm not well-organized personally but I have enough sense to have people around me who are. I'm a good manager."

From the outset, Jordan's role in the White House involved the very matters that were the subject of the recent agonizing reappraisal at Camp David -- personnel and organization.

He was an influential voice in Carter's choice of Cabinet members -- including those who were fired this week. Cabinet heads cleared their deputies and assistants with Jordan, although Carter denied him veto power over selections. The White House organization was also Jordan's responsibility, though it was obviously a reflection of Carter's predilections.

As the new administration progressed, Jordan took on tasks that struck his fancy. He began early to bone up on foreign policy. He tried to plan ahead for the president. He described himself as a political organizer and expediter, a troubleshooter and a private adviser to the president.

His role in the Panama Canal treaties episode was revealing. Jordan was chairman of the White House task force charged with getting the treaties through the Senate and, according to numerous officials who participated in that effort, his performance was invaluable and erratic.

Erratic because Jordan did not provide consistent and constant leadership to the diverse official interests involved. According to associates and senators who were being wooed, Jordan did not make the best use of President Carter or of his other assets in the lobbying effort.

Invaluable because at the one crisis point in the proceedings, Jordan saved the day. When it became clear that the Senate would approve Sen. Dennis DeConcini's now-famous "reservation declaring an American right to intervene militarily in Panama. Panama's dictator, Gen. Omar Torrijos, hit the roof. It looked breifly as though Torrijos would renounce the treaties.

Jordan had befriended Torrijos, and even spent a long weekend with him in Panama. When tensions where highest, he got on the telephone to the general and urged him to sit tight while some face-saving device was worked out. Torrijos followed the advice, and the treaties eventually won two-thirds Senate approval.

Soon after the Panama victory, Carter took his Cabinet and staff to Camp David for a tongue-lashing. This was the first agonizing reappraisal, in April of last year, and it featured a round of admissions that the administration was not working as well as it should.

But that time, too, Carter declined to make Jordan a responsible chief of staff, and Jordan agreed with the decision. Partly, associates say, the young protege felt Carter did not want a chief, and that he, Jordan, was not up to the job.

Partly too, some said, Jordan feared that even if he got the title, he would not the get the power to make the job work -- that Carter would continue to deal directly with Cabinet secretaries and other aides, undercutting any chief's position.

"We might need one," Jordan told an interviewer, referring to a chief of saff, "but there's no one here who can do it. . . I don't have the range of ability to do it. I'm not an administrator. I understand politics but i'm weak on the issues. . . "

The news that Jordan will finally take the chief's mantle seems to please the senior White House staff, among whom he has always been popular. But there is nervousness, too, reflected in a number of conversations yesterday, that Jordan may be too blase about issues, too lazy, too disorganized and too reclusive to play the part of a chief.

"I don't know if he can keep office hours," one associate observed. "I'm not sure he understands how to use the president's power -- or what its limits are," said another. "He may not be smart enough for this," said a third.

But all those who expressed reservations also volunteered that only Jordan was close enough to Carter to pull off the chief's principal duty -- to speak authoritatively fo the president.

Jordan said in a telephone interview last night he knew he had to "organize my staff to compensate for my own weaknesses. I'm not a detail person, i'm a strategy person, and one of the worst mistakes I can make would be to bog down in detail and lose the big picture."

He defined his job as "dealing with the discipline and coordination problem," but vowed he would not "stand between the president and his Cabinet or the president and his senior staff members."

Earlier, on the McNeil-Lehrer Report on public television, Jordan said his job would be to resolve conflicts between the White House staff and the Cabinet "in a middle area of problems. . . . There's been a tendency to take too many problems to the president and involve him in the details of problems that don't really merit his attention."

But he said that because "I do not have the substantive policy back-ground in either domestic or foreign policy. . . differences among the Cabinet and the staff that relate to domestic policy will still be taken first to Stuart Eizenstat and differences in foreign policy will still be taken first to Zbiniew Brzezinski."

Eizenstate and Brzezinski are, respectively, the heads of the White House domestic and national security staffs. Eizenstat said in an interview last night that, while the range of issues going to the president may be reduced by only 10 percent, that "psychologically, it will be important to have Hamilton available to delegate the decision-making authority and to enforce it."

Others in the senior staff said they were taking a "wait-and-see" attitude toward Jordan's exercise of his new power. They agreed, however, that whatever he made of it, Jordan's skills would be an even more important determinant of Carter's political future than they have been in the past. CAPTION: Picture 1, Jordan, right, walks with Ambassador Robert Strauss on White House grounds: "I have my strengths and weaknesses." AP; Picture 2, Jordan with Zbigniew Brzezinski who will continue to handle foreign policy. By Frank Johnston -- The Washington Post; Picture 3, Jordan with Carter aide Gerald Rafshoon and Carter secretary Susan Clough at Futures Farmers of American ceremony. By Frank Johnston -- The Washington Post