Iranian Foreign Minister Sadegh Ghotbzadeh conceded at a news conference today that he has been unable to learn from militants occupying the U.S. Embassy here how many hostages they hold.

Spokesmen for the militants have said variously that 50 or 49 Americans are in the embassy but they have refused to give a complete accounting and they have not explained why visiting U.S. clergymen saw only 43 hostages at Christmas services.

Ghotbzadeh's acknowledgement that even the foreign minister has been unable to pry the information from the militants was further indication that confused lines of authority in the tumult of post-revolutionary Iran are a growing obstacle to liberation of the hostages.

The dispersal of power affects the decision-making ability of officials whose job is to deal with the crisis. As a result, decisions are postponed while the captives, seized almost eight weeks ago, languish in the occupied embassy under the guns of their young Islamic guards.

For the same reason, traditional means of pressure, such as President Carter's call for international economic sanctions, seem to stir little reaction except defiance. Much of the real power here, particularly over the hostages' fate, lies with young revolutionaries or Islamic mullahs only too happy to confront the West.

The young militants have made clear on a number of occasions that they feel no obligation to take orders from, or even listen to, the Iranian government or the Revolutionary Council that in theory sets government policy.

Even among militants involved in the embassy occupation, authority is reported to be vague. Several factions are said to compete for power within the compound and most decisions reportedly are preceded by long and stormy debate.

Ghotbzadeh announced yesterday that he will act as go-between for the militants and the Revolutionary Council, coordinating their stands on the hostage issue. This was interpreted as an attempt to gain more influence over the militants and perhaps moderate their stance. So far, however, he has been unable to find out even how many hostages there are and there is no sign that those holding the embassy are any more willing to cooperate.

The embassy occupiers, who call themselves "students following the imam's line," have throughout the crisis taken orders only from Ayatollah Ruhollah Khomeini, Iran's spiritual and revolutionary leader. Khomeini, who seems to relish the confrontation with the United States and the outrage caused there by the students' hostage taking, has given them no reason to back down.

In his speeches from the holy city of Qom, Khomeini has endorsed the militants' demand that the deposed shah be returned to Iran before the hostages are released. But he also has given his blessing to Ghotbzadeh's idea for an international "grand jury" to expose American "crime" here during the shah's reign.

Until Khomeini makes his thinking on the matter clear to those holding the embassy, the hostages seem likely to remain captive.

Even contrary positions taken by government officials and members of the Revolutionary Council seem to conflict sharply, indicating disagreement among members of the nominally ruling council. It is reported to number 13 members.

Ghotbzadeh reiterated today a warning that, if Carter persists in seeking economic sanctions, Iran might try the hostages as spies rather than present them as witnesses in a tribunal. This seemed to be a departure from his former position, which had urged swift formation of the tribunal and rejected the idea of spy trials as demanded by the students.

Two prominent council members, Ayatollah Mohammad Beheshti and Ajatollahslam Javad Bahonar, said in an interview Wednesday that Ghotbzadeh's tribunal idea had became the consensus of the council, which presented it to Khomeini for approval.

"That idea will be abandoned and the trial of the hostages will begin" if Carter refuses to drop his demand for sanctions, Ghotbzadeh said tonight. i"Unfortunately, the United States has misread our good will and unfortunately has misinterpreted it as a sign of weakness before the pressures of the United States. This has to be changed."

Only last night, however, the Revolutionaly Council spokesman had explained that the real reason Iran is considering dropping the tribunal idea is that prospective members contacted to serve have refused to do so unless the hostages are first released.

Against this background, Finance Minister Abol Hassan Bani-Sadr, also a council member, urged that the hostages be either punished or released. In an interview with the official Pars News Agency, he strongly hinted that Ghotbzadeh -- his replacement as foreign minister and opponent in an upcoming presidential election -- has botched his handling of the hostage crisis.