Ugandan President Idi Amin today forbade Americans living in Uganda from leaving the country, ordered them to meet with him Monday and sent a sharply critical message to President Carter accusing the United States of human rights crimes.

Differing accounts of the purpose of the Monday meeting left unclear how much of a threat it poses for the small American community of about 240, most of them missionaries.

Amin order authorities to prepare lists of property owned by the Americans, including "chickens, goats, pigs and other animals" and he warned that any who were spreading "Zionist Israeli propaganda against Uganda" must "take the consequences." After the meeting, he said, Americans would be free to leave or stay in Uganda.

A spokesman for Amin said later, however, that the meeting "should cause no alarm" because the president merely wanted "to thank all Americans for the excellent work they have been doing in Uganda since the closure of the American embassy" in 1973.

Amin's telegram to Carter accused the United States of crimes that range from racial discrimination and the bombing of Vietnam to the Bay of Pigs invasion of Cuba, the dropping of atomic weapons on Japan and the killings of world leaders by the CIA," Radio Uganda, monitored here, said.

"According to reports from Nairobi," Amin's telegram said, "5,000 American Marines near the eastern coast [of Africa] are supposed to come and rescue 250 American massionaries in Uganda. This is impossible, as the Americans in Uganda are happy and scattered all over the country.In any case, Uganda has the strength to crush any invader."

Last weekend the American aircraft carrier USS Enterprise called at the Kenyan port of Mombasa on the Indian Ocean. That visit had been scheduled long before the current unrest in East Africa and U.S. officials denied that there were any plans to send troops inot Uganda, 700 miles inland.

Amin told Carter that the American president apparently is under "pressure from the Zionists . . . some Zionist Jews who control the news media are the ones exerting pressure."

He added, "I know that . . . it is very hard to remain in that office unless the Zionists put you in their pockets . . . You should be like Field Marshal Amin, who is a black superpower in Africa."

Amin's rambling telegram ended with a request that Carter "pass my greetings on to all Americans, both black and white," said the notation that "I hope to visit you in the White House in the near future."

Most Americans in Uganda are missionaries outside Kampala, the capital. Only about 10 Americans work in Kampala, most of them for Ugandan Airways. There are also said to be a few oil company employees.

The New York Roman Catholic diocese said 72 Catholic missionaries are in Uganda, including 14 different orders of priests and nuns.

The United States closed its embassy in Kampala in 1973 without breaking off diplomatic ties and most of the 2,000 Americans there left after advice that the U.S. government could not assume their safety.

The West German embassy, which represents U.S. interests in Uganda, told Americans today to remain calm, to stay home at night and to avoid provoking Ugandan soldiers. West Germany told Washington it would take all possible steps to protect the Americans.

In an effort to reassure the Americans, a spokesman for Amin said that after the meeting on Monday the president would probably throw a big reception for them. Special honors were being considered for those who had done outstanding work during the "hard period of the economic war," Radio Uganda said.

Amin also directed the Americans to bring statements saying whether they had been harassed in Uganda and he said he would expect them to decide whether to leave the country or continue to work there.

Observers in Nairobi said that Amin's move may be intended to pressure Christian missionaries to leave Uganda of their own accord, Washington Post special correspondent Roger Mann reported. Uganda's Christians, who make up half of the country's populations, have been among the chief victims of recent purges.

Despite what appeared to be an ominous warning to the Americans, observers here pointed out that Amin used similar tactis before. Last year he summoned the 400-member British community for a meeting and ended up reaffirming his fondness for Britain.

Although he is violently anti-Israel - largely because of the Israel raid in July to rescue hostages from Entebbe - Amin came to power partly as a result of training and assistance he received Israeli military advisers.