In the most senstive moment of the three-month hostages crisis between the United States and Iran. President Carter raised the hopes of the nation last night about "postive signs" for a negotiated resolution.

Rumors and reports filled the capital with intense speculation in the hours before his televised news conference, but the president made no announcement of a deal and gave no report on negotiations in progress. He also was careful to close no doors to the Iranian-American settlement arrangements that seems to be shaping up.

Despite the prudent reticence of tight-lipped spokesmen and a tight-liped resident, there was no doubt that the Lanian position was undergoing rapid change and that a United States position designed to meet it is in the process of evolution.

In the eyes of official Washington, Iran's new leader is moving with unexpected and almost unbelieveable speed to make his bid to end a hostage-taking that he never liked but, until now, was powerless to control. One worry here was that President Abol Hassan Bani-Sadr might be shifting the Iranian position to far too fast to be sustained -- and the administration was therefore treading with extreme caution to avoid any word or deed that might trip him up at home.

The international commission of inquiry that Carter guardedly endorsed last night is clearly one part of multifaceted arrangements that are expected to lead in time to the release of the captive Americans. It has long been expected that such "a step toward the resolution of this crisis," as Carter called the commission idea, would play a role in assuaging Iranian passion and wounded pride about the role of America in the regime of the former shah.

More surprising and perhaps more important, although unmentioned by Carter, are three conditions for release of the hostages which have been explicitly directed to the United States by BaniSadr in two press interviews since Monday, and which are reported to have been directed to Washington in private communication also.

The three conditions are: "self-criticism" by the United States regarding its role in Iran since 1953; recognition of Iran's right to obtain extradition of the shah and repatriation of his fortune, and a pledge by the United States that it will never again interfere in the internal affairs of Iran.

Those conditions are by no means simple for a prideful president of a prideful nation certain it has been more sinned against than sinning. Yet compared to the seemingly impossible conditions of a few weeks ago, these are manageable hurdles. On their face, Bani-Sadr's requirements as stated in public are the sort that lawyers can negotiate and resolve with words.

Some news accounts from abroad have quoted Bani-Sadr as saying that the United States must 'admit guilt," something the State Department has said the United States will not do.

But translations of Bani-Sadr's interviews with Le Monde on Monday and on the French program "Face the Public" yesterday have rendered his demand as a requirement that the United States accept "self-criticism."

Such are the gaps that words can cause, and other words can bridge.

No longer is the actual extradition of the deposed shah required in exchange for the hostages, but only the recognition of Iran's right to extradite him. Bani-Sadr made it explicit again yesterday that the body of the shah is not linked to the bodies of the hostages.

No longer are the militant students in control of the future in the occupied embassy, Bani-Sadr has stated clearly that the Revolutionary Council, with the approval of Ayatollah Ruhollah Kohmeini, is to make the decisions and captors are to obey them.

Even the radical students, who have consistently called themselves "Moslem students followers of the imam's [Khomeini's] policy," have acknowledged that they will accept the direction of Khomeini. And yesterday Bani-Sadr said he has Khomeini's approval for his plan to deal with the hostage crisis.

All this rather suddently presented the Carter administration with the best chance in more than 100 days to extract the captive Americans from the occupied embassy and to end the indignity and seeming impotence their captivity has brought.

There is no doubt that much study and discussion has occured behind the scenes and there are hints that maneuvering, if not actual negotiating, has been taking place.

American officialdom, in keeping with what Carter called "this delicate time," is saying nothing about the terms of American counteroffers, or the techniques by which they are being brought to fruition or tried out on the Iranians.

Reporters were cautioned privately, as the nation was cautioned publicly by Carter last night, against excessive optimism. The three-month thriller, one of the most gripping melodramas ever played out on the international stage, is not yet at its climax.

Nevertheless, Bani-Sadr's moves and Carter's cautious public response may signal the beginning of the final act. There were devout hopes in Washington yesterday, mingled with growing belief inside and outside government, that this will be the case.