The Carter administration is preparing to block the sale of three helicopters and a commercial jetliner to the government of Uganda's dictator, Idi Amin.

The decision represents the first clampdown on U.S. trade with Uganda, which Carter denounced last April for Human rights violations that he said had "disgusted the entire civilized world."

Administration sources said yesterday the State Department recommended last week to the Commerce Department that it deny export licenses for three Bell helicopters and a Boeing 707 jet, which were to be shipped to Uganda.

Commerce Department officials were understood to have agreed with State's recommendation. Sources said that after the license denials are issured, the firms have 15 days to respond but thay they, too, are expected to comply without protest.

The helicopters had been ordered directly by Uganda; the used jet aircraft, from a Swiss firm which planned to transfer it on to Uganda, the sources said.

A State Department official declined yesterday to say why the licenses were being denied, but another source said, "Human rights obviously was a factor."

According to a new book called "A State of Blood," by Henry Kymeba, a former high official in Amin's government before defecting to Britain last May, the current regime had killed as many as 150,000 Ugandans.

The administration's action has been sought by Reps. Jim Mattox (D-Tex.) and Donald J. Pease (D-Ohio).

Mattox said last night, "In light of Idi Amin's record of torture and terror, this is surely the only course of action our government can take."

Pease, who had also sought a ban on all commercial trade between the United States and Uganda, said he was pleased with the proposed license denial and called it "a good first step."

Pease has protested the fact that American coffee companies have paid about $200 million in the first eight months of this year for Ugandan coffee, the commodity that provides Amin with his main source of foreign revenue.

The congressman has called for a coffee boycott, but an administration official said last night the government does not comtemplate such an action because it would be counter to free trade principles and could set a precedent.

U.S. imports, overwhelmingly coffee, from Uganda last cost $106.7 million and comprised about 30 percent of Uganda's total trade earnings of $360.6 million, according to the International Monetary Fund. The U.S. import figure is much higher this year because of the rise in coffee prices, but a State Department source said the U.S. share of Uganda's exports is about the same as it was last year.

Pease said U.S. exports to Uganda during the first seven months of this year totaled more than $11 million compared with $6.3 million for all of last year. About 73 percent of this year's sales were in telecommunications equipment such as shortwave radios and field telephones, he said.