While Jeane J. Kirkpatrick, U.S. ambassador to the United Nations, was delivering a scathing speech last October criticizing the government of Ethiopia for its violations of human rights, Reagan administration officials were preparing to send thousands, possibly tens of thousands, of Ethiopians back to their home country.

The Ethiopians involved are largely those who arrived before the 1974 revolution, in which Mengistu Haile-Mariam seized power from Emperor Haile Selassie. Many are the American-educated sons and daughters of the old regime. Although their original visas have expired, they had been allowed to stay on a year-to-year basis because of dangerous conditions in Ethiopia.

The State Department has now determined, however, that the situation in Ethiopia has changed and that many want to stay just because they want to work in the United States or don't like the new government.

In a speech to the U.N. General Assembly Oct. 2, Kirkpatrick denounced the "savagery" of the Marxist Mengistu government, which maintains strong military and economic ties to the Soviet Union.

"According to Amnesty International, it is estimated that some 30,000 persons in Ethiopia were summarily executed for political reasons between 1974 and 1978-- 10,000 in 1977 alone," Kirkpatrick said.

"During the so-called Red Terror, which climaxed in February, 1978, the Ethiopian police and army squads murdered some 5,000 grade school, high school and university students and imprisoned some 30,000 others . . . . Twelve-year-old children were among those immersed in hot oil, sexually tortured or flung out of windows and left to die in the streets," Kirkpatrick said.

"The relatives of the children were prohibited by state edict from mourning, yet at the same time they were encouraged to buy back the body for burial."

Kirkpatrick added that arrests are still being made at the rate of 300 to 400 a week in Addis Ababa alone and "many of those arrested simply disappear and are presumed executed."

But during November, Ethiopians in the United States began to receive letters from the Immigration and Naturalization Service announcing that their temporary status was being revoked "because of the stabilization of conditions in Ethiopia."

The letter said that they should leave the country by the end of the month or face the possibility of deportation hearings. It added that the Ethiopians could apply for political asylum. INS officials said they knew of no instances in which the agency had taken follow-up action.

An INS spokesman said the decision to change the status of the Ethiopians was made at the State Department and that INS was simply following orders.

A spokesman at State said the decision was made last August after the department "concluded that current conditions in Ethiopia are not comparable to conditions in existence during the previous seven years, and the continued granting of blanket special status could no longer be justified . . . .

"The State Department believes that although the situation in Ethiopia has changed somewhat since the 1970s, nevertheless human rights abuses still persist in Ethiopia and some Ethiopians in the U.S. could merit asylum based on individual circumstances," the spokesman said.

But a State Department official said it is "very difficult" for applicants to meet the standards for asylum unless they are well-known political enemies of the Ethiopian government or are related to one. He estimated that fewer than half of those in the special status would be given asylum.

He said that aside from the war zones, Ethiopia is "calm, not pleasant, but calm. It's still a tyranny, but it's peaceful . . . . It's under the thumb of a very nasty dictatorship, but the violence and arrests are not random anymore."

In some cases, he said, it was felt, especially recently, that Ethiopians were coming here on student visas and claiming asylum simply because they wanted jobs or disliked the Ethiopian government and that the change was made to "discourage new or further abuse."

"Political asylum is not granted to someone simply because they do not like their government. It is granted in order to save lives. We don't like that regime either. It's a vile, Marxist regime," the official said.

The State Department would not discuss the apparent inconsistencies in the new policy and the Kirkpatrick speech. A spokesman for Kirkpatrick referred questions back to State.

No one is sure exactly how many Ethiopians will be affected. Ethiopians in this country put the number at between 20,000 and 30,000. The INS spokesman said there are only 2,000 to 3,000, but other government officials believe the number is higher.

As of Oct. 1 last year, before any letters went out, there were 1,232 pending requests for asylum. During the 1981 fiscal year, INS granted only 174 requests for asylum, while 261 were denied.