Radical Islamic students today once again rejected a speedy release of any of the 50 Americans being held at the U.S. Embassy here, directly contradicting earlier statements by Iran's foreign minister that some of the hostages could be home for Christmas.

A spokesman for the students, who have held the Americans captive on embassy grounds for the past 44 days, insisted that all of the hostages will face spy trials before Islamic judges at some undetermined time and said that "none of them will be released before Christmas."

Just 24 hours earlier, Foreign Minister Sadegh Ghotbzadeh sounded a more optimistic note, saying that the departure Saturday of the deposed shah from the United States to Panama made possible a release of some hostages by Christmas. He also said he hoped there would be no trials.

The contradictory positions of the foreign minister and the student captors illustrate a familiar pattern in this revolutionary Islamic nation, whose diffuse and often conflicting centers of power have repeatedly confused the hostage issue.

Time and again during the more than six-week crisis, the students have stood their ground against the Iranian government and the nominally ruling Revolutionary Council, only to have their differences settled -- usually in the students' favor -- by the nation's religious leader, Ayatollah Ruhollah Khomeini.

[In Washington President Carter, speaking at a state dinner for Prime Minister Margaret Thatcher, said "I don't believe" the hostages will be released by Christmas. "The news out of Iran is not good," he added. "The students said 'no' to everything."]

Khomeini has yet to take a clear stand on Ghotbzadeh's comment that the shah's move to Panama represents a "victory" for Iran and, by extension, justifies the release of at least some of the hostages.

In a television interview tonight, Khomeini did not directly discuss the shah's move or the release of Americans, but he appeared to come down on the students' side in their conflict with Ghotbzadeh by recounting their pledge to try the hostages if the shah is not extradited to Iran and saying that the Iranian nation backs this stand.

"The nation agrees with this," Khomeini said. "The foreign minister and the government also agree with this. Why should the nation not support this?" t

Khomeini repeated his now familiar refrain that "the embassy is a nest of espionage and these people are spies."

In their latest standoff with the government, the students invoked Khomeini's name, saying a final decision on a trial for release of the hostages must be made by the 79-year-old revolutionary leader.

Khomeini met today in the holy city of Qom with Ghotozadeh. Neither made a public statement to clarify the issue of Christmas releases or trials. Khomeini used most of his television appearance tonight to continue his now ritualistic attacks on President Carter.

In a television interview yesterday, Ghotbzadeh said that while some hostages could be released in a few days, most of them would remain captive until an international commission was convened to study the alleged crimes of the shah and purported American complicity in them.

Ghotbzadeh named former Amnesty International president and Nobel Peace Prize winner Sean MacBride of Ireland and lawyer Louis-Edmond Pettiti of France as two potential members of the commission. Both men said they had not received an invitation and declined to say yet whether they would participate.

Diplomatic sources said Ghotbzadeh may have trouble attracting persons of international stature to serve on the commission and give it an appearance of legitimacy.

Earlier in the day, Ayatollah Mohammed Gilani, top judge of the First Islamic Tribunal of Tehran, said at a press conference that a quilty verdict against any American hostage could result in a death sentence, a prison term or a fine.

The Ayatollah's mention of a death sentence conflicted with previous statements by Ghotbzadeh, who has repeatedly indicated that nobody would be sentenced to death.

Since the crisis began, diplomatic anaylsts here and in Washington have tried to determine exactly how decisions are made in revolutionary Iran. The students are said to take their orders only from Khomeini, with whom they have contact through the ayatollah's son, Ahmed Khomeini.

But sources reported today that at least once during the crisis the students refused to accede to a plan approved by Khomeini to release three male American hostages who have histories of heart trouble and circulatory problems.

According to the sources, a diplomatic official here convinced members of the revolutionary Council that the three men should be freed to avoid the possibility of their dying while in captivity -- a development that would certainly be blamed on the students.

The recommendation traveled through former prime minister Bazargan and Khomeini's son and was eventually approved by the Ayatollah, who set up a Dec. 5 date for the release. But the students did not free the hostages after some medication was delivered to the embassy.

[At the United Nations, the U.N. General Assembly today unanimously adopted a treaty making hostage-taking an international crime and requiring governments to prosecute or extradite any hostage-takers who enter their jurisdictions, the 'Associated Press reported.]