Col. Mike Hoare, leader of the mercenary force that tried to stage a coup in the Seychelles Islands in the Indian Ocean last November, said at his trial today that the South African government knew about the attempt beforehand and the South African Defense Force supplied his men with arms, according to a transcript of the proceedings made available here.

Hoare handed the court a form that he said was an official Defense Force invoice for the weapons, including 60 Russian-made AK47 automatic rifles, which he said were delivered to his home last Oct. 5. He said senior members of the South African Naional Intelligence Service and military intelligence arranged to provide the arms and told him the Cabinet had approved the abortive attempt Nov. 25 to topple the Seychelles' socialist government of Albert Rene.

Hoare's allegations--which came after two other mercenaries were quoted as saying that they had Pretoria's backing--add weight to persistent reports that South Africa actively seeks to undermine neighboring governments. It is generally accepted that Pretoria supports opposition guerrillas in Angola and Mozambique.

South Africa has strenuously denied any involvement in the Seychelles coup bid. In a speech in December, Prime Minister Pieter W. Botha denied that the government had prior knowledge of the attempt.

The government faces a problem in countering Hoare's allegations, however. The speaker of the South African Parliament ruled in February that the issue could not be debated until the trial was over.

Hoare, who fought as a mercenary in the 1960s in what is now Zaire and is widely known as "Mad Mike," said he was giving his evidence about government involvement "with the greatest reluctance, only because I have no choice."

The trial is taking place in Pietermaritzburg 290 miles southeast of Johannesburg. Hoare and 42 other members of the mercenary force are facing charges of hijacking an Air India airliner to fly them from the Seychelles back to South Africa when the coup failed.

Speculation about possible government involvement began immediately after the episode, when South Africa did not initially charge the mercenaries under its tough antihijacking laws. Under diplomatic pressure from the United States and other Western powers, which warned that air links with South Africa might be severed under terms of the Hague Convention on hijacking, the mercenaries were finally charged in January and brought to trial on March 10.

On the third day of the proceedings, mercenary spokesman Peter Duffy was quoted by Col. Jacob Mouton--head of the Railway Police in Durban, who dealt with the mercenaries when the airliner landed there after the attempt--as saying that "seven or eight" members of the government had known about the coup plan beforehand.

Soon afterward, Martin Dolinchek, a mercenary who was left behind in the Seychelles and is now facing espionage charges there with five others, said in a statement to authorities that he was a member of the National Intelligence Service and had been on an official assignment. This was promptly denied by the service in Pretoria.

Hoare said his initial contact with the intelligence service had been through Dolinchek. He said he later met the head of the service, Alec Van Wyk, who proposed the planned coup to the Cabinet but was turned down.

Hoare said he stayed in contact with Dolinchekand later met the second in command of the service, identified as "Mr. Claassen," who told him the Cabinet had given its approval in principle.

Hoare said that he and Claassen had later met two Army officers, a Brigadier Hamman and a Brigadier Martin Knotze, who had told him the military intelligence service was handling the plan.

Hamman undertook to have the weapons de and a civilian truck arrived with green boxes containing 60 AK47s with folding butts for paratroopers, 15 Hungarian-made rifles, 23,000 rounds of ammunition, 40 hand grenades, 102 rockets and 10 launchers, Hoare said.