Iran's domestic political infighting has moved into a new phase with the ruling Moslem clergy, having long overcome meaningful secular opposition, increasingly split into quarreling moderate and conservative factions.

At the center of the conflict is the crucial question of who will succeed Ayatollah Ruhollah Khomeini when Iran's 82-year-old religious and political leader dies.

Despite recurrent rumors of declining health, Khomeini remains capable of speaking for an hour at a time on television and mocks those who predict his imminent demise. Nonetheless, the succession problem surfaced this winter for the first time since the 1979 revolution with suggestions that a special body be elected to decide whether one man or a collective group should inherit Khomeini's power after his death.

The fact that the question arose at all reflects a behind-the-scenes power struggle carried on with all the ferocity of conflicts over papal succession in the Roman Catholic Church, according to specialists.

They note that until a year ago Ayatollah Hossein Ali Montazeri was assumed to be Khomeini's unquestioned heir apparent.

But despite repeated efforts by Montazeri's friends to elevate him to the status of grand ayatollah, the highest grade in the Shiite Moslem hierarchy, the majority of those who enjoy that exalted status do not recognize him as a peer. That is considered the nearest these conservative grand ayatollahs have come to open opposition to Khomeini, who still commands enormous public support.

As has been true since the overthrow of the late shah, Mohammad Reza Pahlavi, the power struggle continues to hamstring Iran's revolutionary government.

Even during the war against Iraq, the various religious forces have continued fighting for supremacy within ministries. The result has been administrative paralysis, according to specialists.

This has been the case despite the successive elimination as meaningful political forces of westernized liberals, supporters of deposed president Abol Hassan Bani-Sadr and left-wingers who remain capable of mounting as many as five terrorist operations daily in Tehran.

Besides the succession problem, Iran's clerics are divided over land reform, nationalization of the one-third of foreign trade still in private hands, attitudes toward the Soviet Union and further restrictions on the role of women

The main protagonists in the Majlis, or legislature, are Khomeini's supporters, who now are cast as relative moderates and reformers, and the conservative Hojatieh society.

The Hojatieh is a Shiite group that was tolerated by the late shah and originally dedicated to combating the Bahai sect, which it considers heretical. But since last summer the Hojatieh has emerged as a growing political force here. Some knowledgeable analysts are convinced that the Hojatieh, said to control 29 percent of the Majlis compared with their rivals' 25 percent, soon will be in command.

Strict definitions of Iranian clerical factions are risky because various factions often adopt seemingly contradictory stands for tactical purposes. But the rivals do have clear doctrinal differences.

Even when those differences seem obscure to many Iranians, they reflect a constant in Iranian religious history. Shiite Islam, which dominates here, traditionally has been divided between conservatives and reformers and between activists and "quietists."

The Hojatieh are viscerally anti-Soviet and opposed to the burgeoning influence of the pro-Moscow, communist Tudeh Party, which is said to have placed its devotees in critical government positions. Ferreting them out is considered difficult because of their tactic of endorsing Khomeini's every action and their slavish respect, at least on the surface, for Islamic ritual.

But analysts are convinced that Tudeh activists are more adept at gathering information than winning political power. Denounced in the Islamic press, the Communists may become the next victims of revolutionary repression once their key personnel have been identified, according to some analysts.

Backed by powerful grand ayatollahs and their followers, the Hojatieh are believed to be lukewarm at best to the central concept behind Khomeini's rule: the constitutionally enshrined position of Velayat-e-Fagih, or "religious guide." This concept justifies Khomeini's temporal and secular authority in the absence of the Mahdi, or redeemer, the 12th imam whom Shiite Islam holds disappeared in a cave 11 centuries ago and will reappear.

Although theoretically in favor of less clerical activism in government, key Hojatieh followers have gained influential posts in ministries and other official organs, where they have demonstrated their influence by aggressively enforcing strict Islamic codes.

The Hojatieh has strong, traditional links with the politically conservative merchants and opposes various reforms favored by Khomeini loyalists and actively pushed by the Tudeh and other leftists within the Majlis.

So strong has the opposition been that Khomeini issued a religious order authorizing laws voted by the Majlis to take effect even if they are vetoed by the conservative Council of Guardians, which is constitutionally empowered to nullify legislation it considers contrary to Islam.

As one result of the clerical divisions, the president, Hojatoleslam Ali Khamenei, has experienced many of the frustrations that bedeviled Bani-Sadr in office. The Majlis turned down his first choice as prime minister and has declined to restore full presidential power and prestige, especially in the conduct of the war with Iraq.

A foreign analyst who has lived in Iran since before the shah's downfall said, "Sometimes I shut my eyes and think the country is reliving the Bani-Sadr period or indeed even that of the monarchy."

He explained that Khomeini, like the shah, governs through friends, first encouraging groups, then slapping them down when he decides they are becoming too powerful.

"Call it checks and balances or the natural Shia Moslem tradition of infighting and confrontation . . . the end result is the same," the analyst said. "Khomeini . . . has proved himself a past master at riding two horses."