Iran's Revolutionary Council designated to take custody of the estimated 50 American hostages in Tehran, is a mystery-shrouded body split by rivalries that may prolong the captives' ordeal.

Although no complete official list of the council's membership has yet been published, enough information about the group's makeup has emerged to suggest that the fate of the hostages will depend on how the council membership lines up now in a constantly shifting internal power struggle in Iran.

Some of the Revolutionary Council's membership, which is largely dominated by hard-line clergymen, cannot be said to augur well for the U.S. captives.

One of the clerics most recently mentioned in Tehran as a council member is Iran's new revolutionary prosecutor, who last week demanded that one of the captive Americans be handed over to his office for questioning about alleged links with an Iranian guerrilla group.

Analysts generally agree that if the militants holding the hostages at the U.S. Embassy in Tehran go through with their announced intention to turn them over to the Revolutionary Council, this would mark an improvement in the circumstances of their detention and a significant step toward securing their eventual release.

Such a move would eliminate at least one of the main Iranian domestic political rivalries that have blocked progress toward ending the crisis so far.

Nevertheless, a simmering power struggle within the council itself and Ayatollah Ruhollah Khomeini's recent stipulation that the country's figure parliament must decide the hostages' fate indicate that numerous other hurdles still must be overcome. These factors suggest that the captives remain subject to revolutionary Iran's unpredictable, often capricious behavior and its desire to punish and humiliate the United States.

The only thing that apparently can assure the hostages' quick release remains a direct, clear-cut order from Khomeini. So far, he has shown no willingness to give one, and the embassy militants have said their decision to transfer custody of the captives was reached without consulting the ailing 79-year-old ayatollah.

Should Khomeini continue to remain aloof, the immediate decisions on the Americans' fate would depend on how the Revolutionary Council handles its main internal rift: that between the Western-educated laymen installed in key positions and the more hard-line Moslem clergymen who make up the council's majority.

This rift is symbolized by the personal rivalry of Iran's new president, Abol Hassan Bani-Sadr, and the leader of the powerful Islamic Republican Party, Ayatollah Mohammed Beheshti.

Bani-Sadr soundly trounced the Islamic Republican Party's candidate in Iran's January presidential election after Khomeini had barred clergymen from candidacy and the party's weak second choice was disqualified because of foreign parentage. Behesti, who had been touted as a possible presidential candidate before Khomeini's decree, is known to favor more clerical involvement in Iranian politics.

After Bani-Sadr's landslide election with 75 percent of the vote, Khomeini appointed him as the head of the Revolutionary Council in place of Behesti, as well as commander in chief of the armed forces.

But Behesti and his party appear to be in a better position than Bani-Sadr to line up supporters in the Majles, or parliament, to be elected by early April. While Bani-Sadr benefited from Khomeini's tacit blessing during the presidential election, he has not built a party organization that can compete with the network of politically involved mullahs that the Islamic Republican Party commands throughout the country.

Typical of the shifting currents of Iranian politics, Beheshti in early January had indicated a desire to resolve the hostage crisis and get on with the business of shaping post-revolutionary Iran. After Bani-Sadr was elected and began to push that view, however, Behesti backed away from it in what analysts here interpret as an effort to bog Bani-Sadr down in an unproductive pursuit.

"Behesti has an interest in keeping the pot boiling," a knowledgeable American source said.

Regardless of the outcome of Iran's parliamentary elections, referral of the hostage crisis to this body probably would not produce any quick solution, especially given the country's anti-American mood.

"What junior congressman is going to get up and say, 'let's negotiate with the American?'" one analyst asked incredulously.

On the Revolutionary Council, other hard-line clergymen who could frustrate Bani-Sadr's efforts to include Hojatoleslam Akbar Hashemi Rafsanjani. A staunch Khomeini disciple, he was wounded last year in an assassination attempt allegedly carried out by the fanatical Forqan terrorist group.

Ayatollah Abdol Karim Mousavi Ardebili, recently named by Khomeini as the revolutionary prosecutor and reportedly also a council member, has issued a letter demanding that U.S. diplomat Victor Tomseth be handed over to his office in connection with an investigation in Forqan.

Tomseth, who is being held along with U.S. charge d'affaires Bruce Laingen and an aide in the Foreign Ministry in Tehran, apparently signed a diplomatic cable that quoted an Iranian professor as saying some of his former students belonged to Forqan and were "mixed-up kids." This the embassy militants have claimed is proof of Tomseth's complicity with the group.

Another senior clergyman on the council is Ayatollah Mahdavi Kani. He has played a key role in the leadership of the elite Revolutionary Guards and the "komitehs" that have functioned as vigilante gangs all over Iran.

Even the laymen on the Revolutionary Council cannot be relied upon to support Bani-Sadr in a crunch, analysts here believe.

The most prominent of these is Foreign Minister Sadegh Ghotbzadeh, who lost out to Bani-Sadr in the presidential race. Ghotbzadeh has a record of rivalry with Bani-Sadr going back to their competition for leadership of the Iranian exile student movement in Europe years ago.

A leading Iranian moderate said to have retained a seat on the council is former prime minister Mehdi Bazargan. But he is understood to have virtually retired from the chaos of Iranian politics after the embassy seizure Nov. 4 forced him from office.