Two mutinous Ugandan Army units today claimed to have seized a strategic town near the Kenyan border, apparently widening the struggle against the rule of embattled President Idi Amin.

If the town, Tororo, has fallen, it would be a crippling blow to Amin, since the main rail and road routes between Kenya and Kampala, the Ugandan capital 75 miles to the west, pass through it.

There are reports of heavy fighting around Tororo and other parts of eastern Uganda, an area largely unaffected by the war until now.

Meanwhile, a group claiming to represent rebel units of Ugandan air-and sea-borne battalions from the region -- estimated at about 2,000 troops -- issued a statement in Nairobi, Kenya, calling for a general army and popular uprising and the return of former Ugandan president Milton Obote. The statement said two persons were dispatched to see Obote, who lives in exile in Dar es Salaam.

Obote is the leader of one of at least three groups of Ugandans who have brought their opposition to Amin increasingly into the open in recent weeks. Amin's forces have been embroiled in heavy fighting with guerrillas, dissident army units and Tanzanian troops for nearly a month, apparently a crucial phase of hostilities that began when Uganda occupied a 710-square-mile slice of northwestern Tanzania last October.

The most recent fighting reportedly began last night in the military barracks, 1 1/2 miles outside Tororo. According to reports from the area, tanks and armored personnel carriers were stationed throughout Tororo and military aircraft were flying overhead. It was unclear, however, who was in control of the equipment.

The hospital in Mbale, 45 miles north of Tororo, reported receiving civilian casualties.

The rebels appear to be opposed mainly by Nubian mercenaries from the southern Sudan who make up much of Amin's army. There were unconfirmed reports that Ugandan troops from Jinja were blocked as they tried to advance toward Tororo. Troops from Mbale may also have been moved in to try to crush the revolt.

Until now the fighting has been confined to southwestern Uganda where Tanzanians and Ugandan dissidents control the key towns. These forces are said to be moving from their stronghold at Masaka toward Kampala, although there is no information that they are taking part in the Tororo mutiny.

Meanwhile, mediation efforts by the organization of African Unity came to a stormy and inconclusive end today.

The OAU mediation team flew from Nairobi to Dar es Salaam yesterday, to meet with Tanzanian President Julius Nyerere. Told they could not see him until late afternoon, they decided to return to Nairobi and today, they failed to return.

Tanzanian Foreign Minister Ben Mkapa tonight denounced the OAU team for its lack of seriousness.

"It was more important for them to sleep in their pajamas than to meet my president. These people couldn't even sleep in a different hotel for one night and they are supposed to be settling a war where people have been sleeping in trenches for weeks," Mkapa said.

The OAU assistant secretary general, Peter Onu, said in Nairobi, however, that the mediators had "done everything possible to bring about a cease-fire," but they had failed. He said Amin accepted the proposals, but the team was unable to see Nyerere.

In another development, Nyerere has decided not to attend this weekend's meeting in Luanda, Angola, of the leaders of the five "front-line" states that support Rhodesian nationalist guerrillas.