Brief hours after Reuters flashed the text of a purported top-secret message from Jimmy Carter to Ayatollah Khomeini, the Lebanese ambassador to the U.N. commented quietly to friends at a Manhattan party: "It is really disgraceful, but I can believe he wrote it."

That snap reaction by so sophisticated a diplomat to the letter President Carter insists he never wrote -- or even underwrote -- is shared by those here who have watched frantic Oval Office maneuverings in the hostage affair. Trusted officials who have served under Carter see the letter the Iranian government claimed it received from Carter as reflecting the style of the president and his closest political aides.

With foreign affairs specialists supplanted by Carter's political inner circle in managing the hostage crisis, there has been unseemly haste in trying to retrieve not only the hostages but the president's fading fortunes by whispering to Tehran what it wants to hear. The word "disgraceful" used by the diplomat in New York is echoed in Washington, where a sense of shame is growing.

Nobody disputes the White House claim that the "letter" never was written as such. Surely, it includes some rhetoric more familiar to Soviet communism than the Carter White House. But not all parts of the letter. One long-time Carter student who has worked closely with him sees phrases as "pure Carter, vintage Carter from way back. No one in a foreign country could have dreamed that up."

What in the letter is "vintage Carter"? It attacks U.S. involvement in Chile as a "serious example of American intervention." It notes that these actions by earlier administrations have been condemned by Carter. That sounds unmistakably like Carter statements of the past.

So does the charge that "my government inherited a very delicate international situation, product of a different policy, of other circumstances that have led us to commit errors in the past." To knowledgeable colleagues of Carter, that recalled the president's 1977 declaration at Notre Dame that the West should no longer have "an inordinate fear of communism."

Such subtle expressions of Carter's convictions about the contemporary world could not have emanated from national security adviser Zbigniew Brzezinski. Carter associates strongly suggest that Hamilton Jordan, on his mysterious trips to Paris, Panama and perhaps elsewhere, has specifically emphasized this aspect of Carter's world view to persuade the Iranians to free the hostages.

Although Brzezinski's National Security Council staff pulled the early bureaucratic strings in the hostage crisis, Brzezinski now is out on the fringes. The string-pullers today are Jordan and the other intimate political aides brought from Georgia by Carter.

Desperation of the Jordan inner circle peaked after Sen. Edward M. Kennedy broke through in the New York and Connecticut primaries. Moving toward the next primary in Wisconsin last Tuesday, the president engaged himself in a sudden test of will with the Iranian revolutionaries.

With the clock ticking away toward the Wisconsin test, a Paris-based Argentine lawyer named Hector Villalon was clearly encourged to put on paper what he had been hearing, directly or indirectly, from Carter mediators -- including Hamilton Jordan -- about Carter's innocence in the long U.S. friendship with the deposed shah. The White House has acknowledged that Villalon was the interemediary who put on paper the words that the Iranians claimed were Carter's.

But neither the president nor his Georgia insiders wanted either Carter's thoughts (as conveyed to Tehran) about past U.S. sins or his commitment to revolutionary Iran to get into the headlines. When they did, the literally correct denial was made. To hammer the point home, the president conducted an unprecedented personal lobbying campaign among senior journalists here.

The president's frustrating struggle to free the hostages by disavowing America's past goes beyond the "letter" that revealed so much about his true view of the world. In desperately trying to separate Carter from the past, White House political aides ordered the State Department not to invite New York lawyer-statesman John . McCloy, a pillar of the old foreign-policy established, to Carter's state dinner for West German Chancellor Helmut Schmidt.

McCloy's sin: failure to repent his country's alliance with the fallen shah and his pressure on the administration to admit the shah for medical treatment last year. Moreover, as an old cold warrier, McCloy does not accept Carter's edict against "inordinate fear of communism."

It was the first White House party for a West German chancellor missed by McCloy, the postwar U.S. high commissioner to Germany. That blackball was no less symbolic than the "letter" the president never wrote -- the letter viewed here as signaling a "disgraceful" retreat.