Thirteen months after the overthrow of Idi Amin, Africa's most brutal military dictator, Uganda once more has a military government as the result of a slow-moving coup now in its fifth day.

As businesses reopened and this East African capital began to return to normal except for the presence of a large number of Ugandan soldiers, very little is known about the nature of the new government.

It is clear, however, that the military's assumption of power is likely to enhance the possibility that former president Milton Obote, ousted by Amin in 1971, will return to power.

Most of the men in the military commission, expanded from six to 16, are thought to be backers of Obote and most of them come from the northern part of the country where he has tribal support.

One of the commission's first acts was to reverse the ban by ousted president Godfrey Binaisa on the participation of political parties in elections scheduled for December. Revival of the parties favors Obote, who has claimed from his Tanzanian exile that he had nothing to do with the coup. His United Ugandan People's Congress is well-established in the country.

Binaisa, who had no political party backing, wanted all candidates to run under the banner of the United Uganda National Liberation Front, an umbrella group formed to lead the fight against Amin.

The commission has said elections will be held in December as scheduled, but as one diplomat noted, plebiscites carried out by the military have a way of coming out the way the military wants.

It appears, the diplomat added, that Uganda "has swapped one dishonest regime for another," gaining a government that may be less worried about human rights violations like those carried out under Amin when as many as 300,000 people were killed.

Referring to Obote, another diplomat said he intends to become president again, "by election or otherwise."

The commission was silent about its plans today after issuing a 3,000-word statement last night that proclaimed its leadership of the country and sharply criticized Binaisa for corruption, tribalism and incompentence. The Uganda Times, the only daily newspaper, simply ran the text of the statement and Ugandan radio ignored the crisis.

There were reports that meetings were held at the Nile Mansions Hotel, where the commission has set up its headquarters with a number of political factions.

Binaisa reportedly continued to be holed up at the presidential residence in Entebbe on Lake Victoria under guard of Tanzanian soldiers. The last outsiders to see him were British and Canadian businessmen who visited the statehouse last Saturday.

Tanzania still has 10,000 troops in Uganda left here after it led the overthrow of Amin. No coup could have been carried out without Tanzanian acquiescence.

Even though the military move may be embarrassing to Tanzanian President Julius Nyerere, one diplomat pointed out that it might have been even more embarrassing if his troops had moved in to stop the coup.

One notable aspect of the creeping coup is that so far it has apparently been bloodless -- in a country where political violence has become a daily occurrence in the last decade.

A military spokesman indicated however, that the coup's nature could change. He said Binaisa and other former officials may be put on trial "if there is enough evidence," raising fears of possible executions.

Such a move would undoubtedly be strongly opposed by Nyerere, a firm opponent of armed takeovers, and it appears that the military has moved slowly to forestall any counteraction by Tanzania. The military may also try to give a greater civilian cast to the government, whose formation but not composition was announced here tonight.

Nyerere, who apparently was caught by surprise by the coup, has long been close to Obote. It appears that although he may oppose the means used to oust Binaisa, Nyerere will support the likely long-term result -- the restoration of his protege. In any case, the coup appears to have progressed too far for Nyerere to reverse it.

The problems for Binaisa began when he attempted to fire the Army chief of staff, Brig. Gen. David Oyite Ojok, a hero of the liberation war and a supporter of Obote.Binaisa probably wanted to get Ojok out of the way before Obote's scheduled May 27 return to Uganda. But the move backfired when Ojok balked and was supported by other elements in the military.

In addition, bad feelings among the men may have been exacerbated by the fact that Binaisa belongs to the Baganda tribe from the south of Uganda, while Ojok and Obote are both from the northern Lango tribe.

Binaisa apparently misjudged his support among the military and then compounded the error by picking Lt. Col. Samuel Nanyumba as the new chief of staff. That cast the move in strictly tribalistic terms because he was replacing a northerner, Ojok, with a fellow southerner.

Nanyumba in addition, was not well-regarded in the military since he was promoted under Amin and only stopped supporting the dictator in 1977.

Ojok and Paulo Muwenga, the nominal leader of the coup, then used their positions on the military commission to launch the ouster of Binaisa. The commission, an advisory body formed in 1978 during war, had a pro-Obote majority among its original six members including two civilians.

The military has now taken a dominant role by adding 10 battalion commanders to the commission's membership.

As one opponent of the coup said today, "The military has hijacked the government."