Assertions by the White House that the failed rescue mission has resulted in an improvement in the conditions of captivity for the American hostages do not seem to be borne out here in the Iranian capital.

Western diplomats scoff at what they see as the self-serving assertion that breaking up the hostages into small groups and dispersing them increases the chances of the Iranian government gaining custody of the U.S. captives. The dispersal seems, in fact, to increase the danger of the hostages being grabbed and harmed by emotional mobs.

Contrary to statements by President Carter and other White House officials during the week before the abortive mission, the hostages seemed in no immediate danger from any rapid deterioration in Iran's political structure.

Nor has there been any evidence here to substantiate Carter's assertion that Iranian leader Ayatollah Rhollah Khomeini said that he was planning to hold the hostages until after the U.S. presidential elections.

But one American justification for the raid cannot be disputed: no negotiated release of the captives was in sight.

Analysts here pointed out that the U.S. statements on the hostages' dispersal, on political deterioration in Iran and on Khomeini's plan to hold the captives appeared to have been aimed in part at domestic public opinion. According to diplomats here, however, the mission could have been justified simply by the lack of progress in recent dealings with foreign intermediaries freeing the hostages and by the dim prospect that the still-to-be-elected parliament would approve their early release.

The dispersal of the hostages -- if actually carried out as stated by their militant Moslem captors -- almost certainly has resulted in a worsening of their conditions of detention and, in addition, makes it practically impossible for independent foreign observers to examine them regularly.

Regular contact had been hoped for after an International Red Cross team visited the occupied U.S. Embassy here earlier this month and reported seeing all the captives for the first time.

Further, the transfer of the Americans could destroy any rapport built up between them and their Moslem captors in Tehran and thus increase the risk of ill-treatment at the hands of more hostile strangers.

Ironically, however, the disastrous U.S. rescue attempt may have helped clear the way for what must be considered the last chance for a peaceful release of the Americans -- hostage show trials.

While engendering a new flurry of anti-American statements and providing a rallying point for an increasingly divided population and leadership, the U.S. rescue mission for the first time also prompted the militant captors to pose hostage trials as an alternative to the extradition of the deposed shah.

With the U.S. military action and the resulting public outrage on both sides, the militants seem to have achieved what some diplomats here now believe took precedence over the shah's return as the original, main goal of seizing the embassy: destruction of future relations with the United States.

By bringing the two countries to the brink of armed conflict, these analysts feel, the militants can take satisfaction in being able to tar the United States as an aggressor and a plotter against Iran, a view that has been adopted by President Abol Hassan Bani-Sadr.

The militants are intent on obliterating any relationship between Iran and the United States not because they favor closer ties with the Soviet Bloc, these analysts believe, but because they share Khomeini's stated opinion that Iranian links with western, particularly American, culture pose a greater threat to their vision of an Islamic republic than does communism.

In the aftermath of the failed mission, diplomats here say, hostage trials seem increasingly likely. And while there is no guarantee that some of the Americans will not be jailed or otherwise punished as a result, the consensus here is that the trials would allow the Iranian government to take custody of the hostages as a first step and to extract itself from the crisis without losing face by expelling them afterward.

"The only way out is to get them tried," said a European diplomat who staunchly supports the U.S. position. He said he thought that after the new parliament convenes -- probably in about a month if the second round of elections to that body is held on schedule May 9 -- it would promptly order trials for all the hostages with the approval of Bani-Sadr.

"Carter would probably cry blue murder if there are hostage trials, but it's the only way out now," the diplomat said. "I cannot think of any other way."

One reason for optimism that most of the hostages would then be expelled, he said, is that even the militants do not really consider all of their captives "spies" as they often call them. He said the militants have indicated that they consider six or seven of the 50 in the embassy to be spies, along with the three embassy officials living in the Iranian Foreign Ministry.

Diplomats here believe hostage trials probably take precedence in the militants' thinking over holding their captives longer -- possibly until after the U.S. elections -- in an effort to ensure Carter's political demise.

As far as Khomeini's thoughts on the subject are concerned, he has in the past called on the American people not to reelect Carter, but has never publicly linked the holding of the hostages to the U.S. presidential election. Spokesmen for Khomeini and Bani-Sadr have denied that the ayatollah has privately told the Revolutionary Council of an intention to keep the hostages until after the election in an effort to defeat Carter.

"I don't know where Carter got his information," a usually well-informed diplomat said of Carter's statement April 18. "I don't believe Khomeini thinks in those terms."

Equally dubious to analysts here were assessments by Carter and national security adviser Zbigniew Brzezinski in the week leading up to the rescue attempt that a sharply deteriorating Iranian political situation posed new and immediate dangers for the hostages.

In fact, an outbreak of fighting between leftists and Moslem fundamentalists on Iranian university campuses never seemed to bear the slightest relation to the hostage question.

In the nearly six months of the embassy occupation, the hostage issue has taken on a certain stability that has insulated it from other domestic problems. None of the leftist groups on campuses that had opposed the government's order to remove their officers from the universities had ever challenged the Moslem militants' occupation of the embassy, and the government's current conflict with Kurdish guerrillas and its war of words with Iraq have also been divorced from the holding of hostages.

"The fact that the hostages are really irrelevant to the internal situation in Iran was really shown clearly by the university troubles," a diplomat said. i

More likely, he said, was that the Carter administration itself viewed Iran's domestic turmoil as a factor in the timing of the rescue mission.

Serving to justify the U.S. decision to attempt the rescue mission was the open-ended nature of the embassy occupation, diplomats said. They said that while there was no sign of any specific intention to do so, the militants may well have ended up keeping the hostages past November.

"I think it [the rescue attempt] was, in a way, justified because it had become clear a long time ago that the only way for speedy release of the hostages was by this kind of action," a European diplomat said.

However, other diplomatic analysts here saw things differently. One said before the U.S. military action that Washington's best bet for getting the hostages out safely was the most difficult option in an election year: Wait patiently and do nothing.