Uganda Radio confirmed today that President Idi Amin was alive and "fit" as the first full details of the aborted plot to assassinate him were disclosed in this border town by reliable and well-informed Kenyan sources.

Ugandan Vice President Mustafa Adrisi was quoted as saying Amin is "very much alive and very fit."

The broadcast, heard here, made no direct reference to the reported plot, but it did say that the Kenyan and British press had exaggerated the reports of Amin's disappearance "to the extent of hoodwinking the whole world."

The broadcast said the president was on a belated honeymoon with his wife, Sarah.

Amin was tipped off Saturday morning, after the attempted coup was already in motion, and is thought to have escaped with minor injuries. Members of Uganda's State Research Bureau, Amin's feared security squad, have told Kenyan contacts that Amin is presently resting in Nakasero lodge in Kampala, but this has not been confirmed.

The leader of the attempted coup, a Ugandan air force major trained in the Soviet Union and Iraq as a pilot of Mig-21 and Mig-17 jets, reached Busia safely Saturday afternoon and is now believed to be in Nairobi.

The identities of the major plotters were given to me with the request that they be withheld to protest relatives who may still be in Uganda.

The plot was code-named Operation Mafutamingi. Mafutamingi is Swahili for "much oil," but in Uganda, where common folk have been unable to purchase cooking oil for years, it signifies rich people.

The plot was hatched in July of last year when the major met with his brother, an army captain and commander of Kampala's Bombo battalion, and a prominent civilian who would now be Uganda's new president if Saturday's attempted coup had succeeded, the sources here said.

The plotters' organization, the Uganda Liberation Movement, eventually came to include about 500 members of the armed forces, mostly of the predominantly Christian Baganda and Basoga tribes. Amin and most senior members of his government and armed forces are Moslems of northern Uganda's Nilotic tribe.

For the past year, the sources said, the major and his brother seized every opportunity to hijack and pilfer a wide range of weapons from the armed forces. They stored the weapons in a Kampala shop owned by a prominent businesswoman, who also fled to Kenya Saturday.

The sources said the plotters used the password Kizito, a common Basoga and Baganda name, to identify one another. An engineer in charge of transmission at Kampala's telephone exchange facilitated smooth and candid communications among members of the Uganda Liberation Movement. He arrived in Kenya Monday, the sources said.

The Movement was concentrated in Kampala's Bombo battalion and at the Gula air force base in northern Uganda, but there was scattered military support elsewhere as well, according to the sources at the border.

By their account, the plot leaders met in the Kampala shop where the weapons were stored Friday and completed their plans to assassinate Amin and topple his government the next day.

Four ground units as well as air force bombers were to take part in a massive 1 p.m. attack on Entebbe lodge, where Amin was to meet with the Cabinet. A sympathizer in the State Research Bureau kept the plotters aware of Amin's plans, the Kenyan sources said.

The first unit, made up mostly of low-ranking Basoga and Baganda soldiers, set off from Kampala at about 4 a.m. Saturday with a cache of weapons, which they deposited in an Entebbe shop 25 miles away.

They hid in a wooded area near Entebbe, but by dawn news of the plot reached Amin. Because it was Saturday, and most loyal officers were not at their posts, he was unable to react quickly or with a large force, the sources said.

By midmorning, when the first unit had picked up its weapons, Amin had not yet acted. About then, the coup leaders learned that Amin knew of their plans, but it was too late to retreat, and the second unit began advancing from Kampala to Entebbe.

Unable to raise the defenses he needed, Amin, wearing a bullet-proof vest and accompanied by a sizable military entourage, tried to escape to Kampala but ran head-on into the plotters' second unit on the outskirts of Entebbe, according to the sources' account.

Gunfire was exchanged, and Amin may have been wounded. Survivors warned the major, who was still in Kampala, to flee.

With a lieutenant, three sergeants, a private and two civilians, the major took off by road toward Busia. The group carried four Soviet AK-47 automatic rifles, handgrenades, a rocket launcher with many rockets and two Israeli-made field radios.

They reached Bulega in Kenya about 4 p.m. after passing undetected through roadblocks hastily erected by Amin's air and naval battalions. They went immediately to the Among'ora primary school and asked Kenyans there to call the police.

Busia police arrived at 7 p.m., accepted the readily surrendered weapons and interrogated the defectors at the Busia police station. During the questioning, a car of five Uganda Liberation Movement civilian activists, including the owner of the Kampala shop where the weapons were stored, arrived in Busia, the sources said.

All 13 were escorted to Kakamega, Kenya's western provincial headquarters that night. It is assumed that they have now melted into Nairobi's large Ugandan refugee community.Their weapons were taken to Nairobi.

None of the 13 who reached Busia knew what had happened to Amin, but Ugandan security officers told Kenyan friends that he "sustained minor injuries in an auto accident between Kampala and Entebbe and is now resting at Nakasero Lodge."

There are widespread rumors that many Baganda and Basoga soldiers were killed Saturday and Sunday, but these have not been confirmed. There are also rumors that Baganda and Basoga people in their own regions are being beaten and their houses looted by soldiers. This type of activity by soldiers has been commonplace in Uganda for the least three years, however.

According to a Kenyan who works on the Ugandan side of the border, uniformed soldiers have been combing the area since the weekend.