An atmosphere of quiet confidence in the White House reflects President Carter's changing status as measured by the Opinion barometers. They are not cocky, the men and women the president brought into government. They are saying we are not up all that high, just as we were not down so low as you in the press reported six months or a year ago.

This last says a lot about the Carter presidency at the end of the first two years. Jimmy Carter was a newcomer, almost an accidental president. In a nation fragmented by past disasters - Vietnam, Watergate, the recession - he had no constituency in the real meaning of that word.

But he has created a following that will stand him in good stead for the rigors of the second two years. It is a following that, short of some disastrous turn, could see him through to renomination and reelection. That is a far distant view, given the time of troubles in which we live.

His loyal lieutenants, citing his achievements in the foreign as well as the domestic field, can odd others to the Camp David summit. One was the Panama Canal and the fierce struggle to turn the canal eventually over to the Panamanians, won by a single vote. Another, less spectacular, yet important in strengthening the defenses of NATO, was the resolution of the Cyprus dispute so that the Turkish arms embargo could be lifted.

By standing up to Congress on spending issues, he cannot lose, given the present mood of the country. Vetoing the defense appropriation bill, he eliminated the proposed $2-billion nuclear-powered aircraft carrier. While the Defense Department did not get the subsititues to fill in the $2-billion gap, the public was certainly not going to weep over an expenditure the wisdom of which, in strategic terms, was disputed.

The president's victory when the House failed to override his veto of the $10.2-billion pork barrel bill was a happy end of the intensive efforts he had put into sustaining the veto. Carter himself made 60 telephone calls to House members and his wife, Rosalynn, made nearly 100.

Even if he had lost, he would have had public opinion with him, given the obsession with economy is government. That full-page of Howard Jarvis, father of Proposition 13 in California, may have been the clincher. Voting for pork-barrel projects was comparable to original sin.

Looking ahead, the same confidence prevails. Perhaps as early as November 1 a SALT II agreement with the Soviet Union will be reached. Shortly afterward President Leonid Brezhev will come to Washington for the official signing in the full blaze of television.

If everything goes according to present plan, the president will go to the country with one of the most important speeches of his career. He will make the case for SALT III and a mutual and substantial scaling down of the vast stores of nuclear weapons with an overkill capacity sufficient to destroy both superpowers, and for that matter the rest of world, two or three times.

One reason for the president's confidence in a new SALT agreement is the evidence that Soviet spending equal to roughly 15 percent of gross national product. That is at a time when Soviet citizens are increasingly consumer-conscious. They want the good things of life that, despite all the barriers the state puts up, they know the West enjoys.

There are no illusions in the White House about the difficulty of winning Senate ratification by a two-thirds vote for a SALT treaty. But the president has faith in his own power of persuasion and the support he will get from the joint chiefs of staff and his secretary of defense, Harold Brown. During the struggle over the Panama Canal, support for the administration's position in the polls was a low ebb. That is in contrast to opinion polls on SALT which have consistently shown a support of 60 to 70 percent.

At a rough estimate, the conflict over ratification will take from two to three months after the new Congress convenes in January. At least one of the bitter-end opponents has indicated that he will filibuster if necessary to block a treaty. One asset for Carter is he warm and close relationship with Majority Leader Robert Bryd, for whom he has unbounded admiration.

The image-makers are having their day at the White House. But Carter's own frank realization of the errors he made when he first came to Washington is responsible for the change in atmosphere. He had run against Washington and he was bent on holding himself aloof from the temptations of this latter-day Rome.

He seemed cold, remote, self-righteous in that first year. Now, with the help and encouragement of Rosalynn, he is working to change all that.