Ayatollah Ruhollah Khomeini, the Moslem holy man who leads the religious opposition to the shah of Iran, charged today that a plan exists for an American-backed military coup that would lead to a massacre of his followers, according to a close aide.

The charge seemed to reflect concern by Khomeini that victory, with the shah about to leave the country on an extended "vacation," may be snatched from him by the Iranian military.

The allegations came in an interview with one of the two Khomeini aides who regularly deal with the news media on his behalf and serve as his interpreters with reporters.

Sadegh Ghotbzadeh said in the interview that if a military coup is permitted, the long-range consequences for the American strategic position in the Persian Gulf would be incalculable because the mainstream opposition to the shah would have been proven wrong in its belief that it could oust the regime without communist support.

Khoumeini said in an interview with Italian state television today that he fears the generals plan to take over the country on the shah's behalf when he leaves the country.

Ghotbzadeh said Khomeini had alerted the population and urged it to stock as many arms as possible to resist the army and, in the aide's words, "to blow everything up if there is a coup." That seemed to be a call to sabotage Iran's oil industry, the basis of its wealth and of its economic interest to the West.

The Khomeini aide rated as 50-50 the chances that the military plot would be carried out and implied that this depends largely on the U.S. attitude. He dismissed the chances for success of the civilian government of Shahpour Bakhtiar, who has been rejected by Khomeini.

The aide named the three generals who would head the coup and establish a military junta as Khosrou Fardoust, who controls the Imperial Guard, Abbas Gharabaghi, the chairman of the joint chiefs of staff, and Jafar Shafeghat, the minister of war. Ghotbzadeh listed five other generals as members of the plot.

Ghotbzadeh said the reason that the highly popular Gen. Feydoun Jam had refused to serve as war minister in the current civilian Cabinet was pressure from fellow officers who insisted that he step aside for a general more friendly to the shah.

Khomeini regularly receives reports from Iranians who call on him at his exile headquarters near Paris. The intelligence his followers have been gathering for him seems to have been generally accurate in the past, if the success of his previous tactical directives to his mass following in Iran is any indication.

Since all of the generals allegedly involved have a long history of association with the U.S. military, the aide said no one would believe that such an operation could exist without American knowledge and approval.

In a scarcely veiled hint that the ayatollah's movement would be forced to turn to the neighboring Soviet Union for help in case of a coup, he said, "If we are defeated by a military coup the argument that we need money, weapons and external support becomes valid. Then the communists will be accepted. This is the real danger."

The aide said that Iranian Communists have always argued with members of Khomeini's movement that to win out over "American and British imperialism," the backing of the only viable counterforce, the Soviets, was necessary. Khomeini's followers consistently rejected this view, Ghotbzadeh said.

He said Khomeini recently had softened his view that the United States is inevitably his adversary. Since receiving reports of the military plot, however, his suspicions of Washington's intentions have been aroused anew.

Ghotbzadeh said that while the ayatollah's attachment to the basic principles of a government faithful to Islamic ideas is constant, his thinking about the forms of government has evolved since he came to France last year. Khomeini's preference now would be for a parliamentary democracy along Western European lines, as in West Germany or Italy.

The reason for this evolution, Ghotbzadeh said, is that Khomeini has been able to consult with many more people here than he could during his previous period of exile, when he was living largely isolated in Iraq, Iran's authoritarian Arab neighbor.

Khomeini has stressed in recent statements his acceptance of modern economic development. Apparently disturbed by a number of recent articles in major U.S. publications depicting him as a medieval obscurantist, Khomeini has been giving a series of interviews this week to the three major American television networks. He recorded a CBS "Face the Nation" interview for broadcast on Sunday.

The aide said that even Khomeini's statements that Iranian oil will no longer be sold to South Africa or Israel have been distorted. The reason that an Iranian government close to Khomeini would cut off oil to Israel, Ghotbzadeh said, is that Israel has been so closely identified with the repressive side of the shah's rule.

"Otherwise," he said, "we would most probably have continued to supply them oil, especially in light of Arab hostility or indifference to our movement."

The aide alleged that the Israelis, who are known to have helped organize SAVAK, the Iranian secret police, have taken part in torture of members of Khomeini's movement and have developed and supplied sophisticated torture instruments.

"Israeli embassies have been even more active in slandering us than Iranian embassies," Ghotbzadeh said. "We are against Israel for different reasons than people think."

Thotbzadeh insisted that, contrary to reports, there is no Libyan or Palestinian money backing Khomeini. The aide said the Ayatollah had agreed to meet a month ago with Libyan and Palestinian emissaries because he was seeking information on the fate of one of his top followers, Imam Mussa Sadr of Lebanon, who disappeared Sept. 30 at the end of a trip to Libya.

CBS News also reported:

In an apparent shift of position, Khomeini said in an interview that he would direct the new government of the Islamic state he predicts will be established in Iran within a "few days." Khomeini told an interviewer that "I will supervise and direct the government." When asked if he would, in effect, be the strongman of Iran, he replied, "You may assume so."

In the past Khomeini has repeatedly insisted that he had no intention of leading a new Iranian government or "be part of it."