It was an awkward moment for White House press secretary Jody Powell.

At a briefing last week, Powell was asked about the apology of Brady Tyson, an American delegate to the U.N. Human Rights Commission in Geneva, for the United States' involvement in the overthrow of the Allende government in Chile.

Why had the State Department disavowed Tyson's statement, and why had President Carter called it "inappropriate," the questioner asked, when during the second campaign debate last fall Carter had said much the same thing.

"The only distinction I can draw, which is a fairly tortuous one, is the difference between what the impact of the statement made during the campaign was and the statement made as President," President," Powell replied with a grin.

In the first seven weeks of the Carter administration, the President and his aides have had ample opportunity to witness that difference in impact, and the restraint that it imposes.

It is the difference between candidate Jimmy Carter charging that the Republican administration "overthrew an elected government and helped to establish a military dictatorship," and President Jimmy Carter feeling constrained not only to call Tyson's apology "inappropriate," but to note that "the Church committee in the Senate has not found any evidence that the United States was involved in the overthrow of the Allende government in Chile."

Carter, as President, was noticeably more restrained than he had been as a candidate. But that has not always seemed to be true during these first weeks of the new administration.

Perhaps the best example of this, which also occurred last week, was the President's use of the phrase "defensible borders" in connection with a Middle East peace settlement. The phrase has long been used by Israel in arguing against returning all of the Arab territory it captured in the 1967 war.

Carter used the phrase several times during the campaign, to no one's apparent consternation. But when he invoked it on the South Lawn of the White House while welcoming Israeli Prime Minister Yitzhak Rabin, it threw the diplomatic community into a mild tizzy of interpretation and analysts of possible shifts in U.S. policy.

The White House quickly said there was no shift. It seemed at once unpreturbed and mildly amused by the uproar.

In the wake of these developments, two things seemed clear. First, that Carter, like any candidate turned President, no longer enjoys the luxury of having his words passed over as mere campaign rhetoric. And second, unlike many of his predecessors, when Carter speaks of foreign policy he will not feel constrained by what one White House aide called "the jargon" of diplomacy.

In the White House, the attitude toward the traditions and niceties of diplomacy borders on contrempt. Aides speak of "the language of a dying race" and of "code words designed to be understood only by the select few."

"I share his (Carter's) inclination to dispense with all that," said Powell, who at one briefing made a passing reference to "folks in striped pants."

"It's a holdover from the time when nobody ever said what they meant," he added.

But if the President is going to dispense with diplomatic code words in his public statements, his aides caution against interpreting this as merely blurting out whatever comes into his head.

"The thing that everybody told us when we got here was that we had to be much more careful in making statements, that everything he said would be weighed and would have an impact," one official said. "That has turned out to be true. But Carter still speaks his mind when he feels like it. He is not noticeably more restrained than he was during the campaign."

The same official added: "He doesn't say things that he doesn't mean."

Carter is a supremely self-confident man, at ease with language and its uses. In almost two months in office, he has delivered only two prepared speeches - the inaugural address and his televised fireside chat. All the rest of his public statements have been based on prepared notes, and in several cases he has ignored even these.

Powell said White House officials are keenly aware of the new impact of Jimmy Carter's words. He attributes this to a tendency to "overplay" and "overinterpret" every presidential utterance. But if Carter no longer is free to make the kind of statements he did during the campaign, neither is he about to change his style in saying what he can and wants to say now, Powell said.

"I think that in terms of the substantive portions of his statements, you will find that he has been quite careful," the press secretary said.

"But you can't have a generally accessible and free-wheeling contact with the press and read memorized little phrases . . . Basically it all goes back to his belief that when you get ready to do something important in foreign policy, you have to let people generally know what you want to do, why you want to do it and how you propose to do it."