President Idi Amin of Uganda broacdast a claim today that tank-led Tanzanian troops have stranded him at his Entebbe residence, but Tanzanian officials here branded the report as nonsense and said their forces are not even in Entebbe.

Diplomatic sources in Nairobi, Kenya, suggested the broadcast could be another of the Ugandan leader's antics, designed either to set the stage for triumphant victory claims in the next few days or to distract attention from a reported revolt within his own hard-pressed army.

The broadcast was part of an increasingly confusing picture of sporadic fighting, claims and counterclaims in the four-month struggle by nvading Ugandan exiles, backed by nvading Ugandan exiles, backed by Tanzania to topple the unpredictable, brutal dictator who has run Uganda since taking power in a military coup in 1971. Adding to the confusion were unconfirmed reports he actually has fled to an isolated area of Uganda, or even left the country.

Residents of the Ugandan capital of Kampala, contacted today by telephone from Nairobi, reported "heavy fighting" in the streets. A woman in the office of an international agency said excitedly that everyone else had evacuated the office and she could see combat below her window.

Amin's British-born adviser, Bob Astles, said a dozen Tanzanian tanks had surrounded the Ugandan state house at Entebbe, 25 miles south of Kampala, and that Amin was trapped inside prepared to "fight to the end."

"Even if he is cut off from all his family, including his children, he will use any type of gun to the maximum to see that he makes a breakthrough and reuntites" the country, despite the fact he has with him only 20 aides, the Kampala broadcast said. Amin was quoted as saying he will "show how only 20 men can fight against 20,000 enemy troops who are attacking Uganda."

But Tanzanian officials here said the Tanzanian-backed forces seeking to overthrow Amin are still at Mpigi, overlooking Kampala and Entebbe, which they occupied late last week. They speculated Amin may instead be fighting rebel forces from his own army and blaming it on the Tanzanians.

Unconfirmed reports from diplomatic and Ugandan exile sources in Nairobi tell of a coup attempt led by Maj. Gen. Ephriam Mondo, Uganda's minister of state for defense. According to these reports, Mondo, at a Defense Council meeting yesterday, ordered Amin to step down and Amin refused. A gun fight followed, sending Amin and his followers fleeing to Entebbe and prompting Mondo's forces to take up positions in Kampala, they said.

According to a knowledgeable observer, Mondo has close relations with the Kenyan government and had been fingered by Kenyan authorities as a desirable replacement for Amin. Kenya reportedly was behind a Mondo-led coup plan that failed to come off as scheduled about three weeks ago.

The Kenyans are known to be worried that Tanzania might try to install former Ugandan president Milton Obote as Amin's successor. Obote, a close friend of Tanzanian President Julius Nyerere, has the largest force of Ugandans fighting against Amin.

Recently, however, the Tanzanians have privately cooled on Obote, believing he does not have enough popular support within Uganda. Nyerere has argued repeatedly that Tanzania does not intend to impose Obote, or anyone else, on Uganda. The Tanzanian president has been working to forge unity among the diverse anti-Amin organizations.

Ugandan opposition forces meeting today in the northern Tanzanian town of Moshi publically agreed to bury their differences and form a "Uganda National Liberation Front" headed by an 11-member executive committee. Its chairman is Yusufu Lule, an elderly, highly respected Ugandan educator. The other members, all leading Ugandan exiles, include people a wide range of political views from Marxists to capitalists to conservative monarchists.

In its first public statement, the Front declared its aim is to establish "a firm basis for national unity" and "coordinate efforts" aimed at overthrowing Amin. It pledged to organize democratic elections based on universal suffrage.

Tanzanian officials have expressed concern privately that the military campaign would "get ahead" of the drive toward political unity. They have been worried that Amin could fall before a transitional government is established, leaving a power vacuum in Uganda.