Former Ugandan President Milton Obote said yesterday that a network of resistance cells has sprung up all over his country to overthrown the harsh regime of Idi amin.

In an interview, Obote acknowledged that it would be a "formiable task" to oust "Amin and his fellow gangsters."

Yet the former president, who was deposed by Amin in 1971, declared, "The resistance has tremendous hopes of success" in time. Small groups and individuals, he said, have already struck down some of Amin's more notorious killers although several attempts on Amin himself have failed.

Obote, a trim 52, spoke in the lounge of the London hotel where he is briefly staying. He came here to prosecute successfully a libel suit against Judith Countess of Listowel, author of a laudatory biography of Amin.

Since his overthrow in January 1971, Obote has been living in Dar es Salaam where he looks after 20,000 Ugandan refugees who have fled to Tanzania. The government of President Julius Nyerere pays his expenses.

Obote clearly hopes to return as president to Kampala but he has been reluctant to speak until row for two reasons. His Tanzanian hosts, like all African states, are formally opposed to any interference in their neighbors' affairs, even in a government as noxious as Amin's.

Secondly, as Obote observed grimly as he stood to say goodbye:

"This particular interview will cause thousands of killings. Because I have spoken, therefore I have informants inside Uganda. He [Amin] will go to my village, my area. . ."

Apparently, Obote has now reached a decision that the price is worth paying to reach a wider audience.

Obote said that the resistance in Uganda has a central head, but declined to locate it or even to name the movement. It has no underground newspaper, he said, but issues leaflets from time to time.

He stressed that the assassination of Amin alone would not end his country's nightmare.

"You remove Amin and the system continues," he said. "Therefore you must remove the system, Amin and his fellow gangsters. If you remove Amin you only remove the idiosyncracies of Amin."

He estimated that Amin and his henchmen have killed "hundreds of thousands of Ugandans," in what amounts to a campaign of genocide.

"In 1971," he said, "the massive killings were concealed and confined to two tribal groups, Acholi and Lango. Now it is everybody, including Amin's own area," the northwest and its Kakwe tribe.

The murders, Obote said are undertaken to wipe out potential political enemies, to suppress plots, real and imaginary, to further smuggling rackets and the like. Entire villages suspected of harboring a fugitive have been wiped out to the last infant, Obote said.

"Corruption and graft are the basis of the regime." Obote said. "That is why the Asians were thrown out, to seize their property cheaply."

Obote, a former schoolteacher and once head of Uganda's biggest political party, concede that Amin has a strong military base.

"Amin has recruited an entirely new army, mostly loyal to him, all foreigners."

It includes Zairians, men from the south Sudan and so-called Nubians, Sudanese who came to East Africa in the last century with European explorers.

Obote sidstepped all questions about his own links to the resistance. He did say with a grin that, "I have given them my blessing."

As others have reported, Obote said Amin has looked on while victims were tortured or killed and sometimes pulled the trigger himself.

His most prominent victim, Obote said, was the Anglican archbishop, Janani Luwum. He was seized last Febuary and forced to kneel at Amin's feet. Instead of begging for mercy, the archbishop prayed. so, according to Obote, Amin shot him dead.

Amin has ruined Uganda's economy Obote said, and peasants live on what they grow for themselves. They have no cash to buy sugar, salt, clothing or the simplest manufactured articles.

"Most people are walking in rags," Obote said. "My own mother and my own sister who live in a village have one dress between them. When one goes out, the other must stay in."

The coffee export crop is seized (when it isn't smuggled) to finance high living for Amin and his aides. Amin now pays his prostitutes in dollars and pounds. Obote said, and sends his mistresses on shopping sprees in London and Paris.

Obote, like some specialists in the field, is convinced that Amin's coup was masterminded by a foreign power. He declines to name any, but notes that high-ranking Israeli officers were much in evidence at the Kampala airport on the day in 1971 that Obote was scheduled to be assassinated.

"Uganda has suffered. Israel has suffered," Obote said. "My concern is to the future not to rub salt in old wounds.

Former CIA officials who have becos critical of the agency have said that Mossad, the Israeli intelligence, service, was the spearhead of a plot worked out with the British Secret Intelligence Service and Langley. In 1971, Obote was regarded as a dangerous socialist who was embarrassing Britain in particular over Prime Minister Edward Health's insistence on selling arms to South Africa.

If Israel did install Amin, Jerusalem paid dearly for it. Amin threw out a corps of Israeli military advisers and slaughtered scores of gandan officers they had trained.

Obote and two of his aides leave London about $125,000 richer than when they came, at least on paper. A jury awarded them this sum for Lady Listowel's libel. She says she is broke so the Ugandans may never see much of it. Any money they receive. Obote said, would be turned over to help the refugees in Tanzania.