Iranian students and Revolutionary Guards loyal to Moslem leader Ayatollah Ruhollah Khomeini continued to hold an estimated 60 Americans hostage at the U.S. Embassy here today to back demands for the extradition of the exiled shah, as other students seized empty U.S. consulates in the Iranian cities of Tabriz and Shiraz.

Pro-Khomeini students and Revolutionary Guards also occupied the British Embassy here for five hours today.

The two U.S. consulates -- seized following a call by the 79-year-old Khomeini for action against "the great Satan, America" -- had been closed, along with a third in Isfahan, during the revolution earlier this year.

In Tehran, Ahmad Khomeini, the son of Iran's revolutionary leader, called for the severance of all political, economic and cultural relations between Iran and the United States.

Iranian Oil Minister Ali Akbar Moinfar was quoted as saying he was prepared to cut oil exports to the United States if Ayatollan Khomeini gives him the order.

Pressured by the ruling clergy's mounting demands for action against American interests while the deposed shah is undergoing cancer treatment in New York, the Iranian government announced the cancellation of two treaties with the United States and the Soviet Union.

Ahmad Khomeini made his recommendation during a press conference in the U.S. Embassy after talks with the students, who yesterday seized control of the mission with the cooperation of Iranian authorities.

There was initial speculation that the talks between Ahmad Kohmeini and the students might produce some initiative toward ending the embassy occupation, but he gave no sign of acting in such a capacity.

The continued occupation highlighted the weakness of Prime Minister Mehdi Bazargan, who has been the target of sharp clerical criticism for his recent meeting with U.S. national security adviser Zbigniew Brzezinski in Algiers. The criticism has put Bazargan under new pressure to make good his repeated threats to resign.

Ahmad Khomeini said that continued relations with the United States would be acceptable if they were on the same basis as with any other country, but that if the United States acted as an imperialist power, the ties would have to be cut.

Answering questions about the position of Bazargin, Ahmad Khomeini reiterated complaints against him aired in recent weeks by other members of the clergy.

Ahmad Khomeini left the possibility open for Barzargan's resignation by commenting simply that Bazargan had not seen Ayatollah Khomeini since his return from Algeria two days ago. There would be no question that Bazargan could not resign without the ayatollah's consent.

During the press conference, the students reiterated that their first demand of the Unite States was the extradition of the shaw, but they added that their basic aim was to rid the Middle East of "U.S. and Zionist influence."

The students also expressed dissatisfaction with the reaction of the U.S.

government to their occupation of the embassy, charging it with trying to pretend that the matter was not serious.

They warned that the seizure of the embassy and personnel was only the start of action against the United States, but showed no sign of having mapped out any subsequent strategy.

The short-lived takeover of the British embassy began at 6 p.m. local time when more than 100 students stormed the building and herded diplomats and their wives and children, who live in the embassy compound, into one building.

Armed Revolutionary Guards then arrived on the scene and occupied the embassy. One of the guards said they had taken over the building to prevent it from being stormed by unauthorized groups.

The militiamen swarmed over the walls of the embassy in several different places simultaneously and swiftly took control of the compound from the students, who had detained as many as 30 British diplomatic staffers in one of the embassy residences. About five hours after moving in, the militiamen returned the embassy to the control of British diplomats.

Britain has been the target of hostile comments by Ayatollah Khomeini and others for its alleged support of the shah's last prime minister, Shah-pour Bakhtiar.

Bakhtiar currently lives in France, but had been allowed to visit Britain and make public appearances to attack the revolutionary authorities in Iran.

The takeover occurred despite appeals from students occupying the U.S. Embassy for the second day that their protest should not be extended to other diplomatic missions.

Tens of thousands of students surrounded the U.S. Embassy compound today shouting anti-American slogans such as "Death to America" and "The embassy must be destroyed."

The official Paris news agency meanwhile, reported that an American, identified as Bill Herr, had been taken hostage in the southern oil town of Ahwaz by members of the local rural development office.

The students at the U.S. Embassy showed reporters photographs of the hostages, including women blindfolded and with their hands tied.

They said reporters would not be allowed to speak to the hostages until they had been interrogated.

"The women are being held separately from the men. They are being well treated and well fed. We are treating them in a humane way but not a brotherly way," said a student spokesman.

He said that the Iranian staff had been released and that the hostages included Americans, Pakistanis, South Koreans and Bangladeshis.

The U.S Embassy takeover, which has the backing of Iranian clerical leaders, appeared to threaten Bazargan's already weakened provisional Cabinet. Telecommunication Minister Hassas Eslami announced today that he was quitting and the health minister resigned last week, citing the government's disorganization.

Government spokesman Sadeg Tabatabai said "[The U.E. Embassy occupation] is a natural act and a natural reaction by the nation when the American government pays no attention to the nation's just demands or else rejects them."

He was referring to a government request for the extradition of the deposed shah, which the Foreign Ministry said was made Oct. 30.

The shah flew to the United States from Mexico last month and is under going treatment for cancer in New York.

The messages of support for the students from government offices and other institutions were broadcast to the demonstrators outside the embassy through loudspeakers mounted over the main gate, accompanied by demands for further action against U.S. interests.

Among the more prominent demands was the halfing of all crude oil supplies to the United States, which currently receives 600,000 to 800,000 barrels a day of Iranian crude.

In a separate measure that might have saved the government criticism if taken earlier, the Foreign Ministry announced today that Iran had cancelled a 1959 defense and Mutual Cooperation treaty with the United States and two chapters of a 1921 treaty with the Soviet Union.

Both agreements had been under scrutiny for some weeks, and a recommendation for this action had been sent recently to the Revolutionary Council for approval.

The opening clause of the U.S. treaty stated, "The imperial Government of Iran is determined to resist aggression. In case of aggression, the government of the United States, in accordance with the Constitution of the United States, will take such appropriate action, including the use of armed forces, as may be mutually agreed upon and as is envisaged in the joint resolution to promote peace and stability in the Middle East."

The parts of the Soviet agreement to be scrapped gave the Soviet Union "the right to advance her troops into the Persian interior" if a third party should "desire to use Persian territory as a base of operations against Russia."

Abrogation of the U.S. treaty cornerstone of the shah's relationship with the United States, is unlikely to have significant impact on the present surge of anti-Americanism, which is carrying the government before it.