Rhodesia's security forces reported killing 90 black nationalist guerrillas throughout the country during the past 48 hours in a drive to create an effective "blanket of security" for next week's elections.

The toll, which is the second highest of the seven-year-old war, was announced today by the country's top military commander, Gen. Peter Walls, to a large gathering of foreign correspondes here to cover the elections for Rhodesia's first black-led government.

The general also asserted that the Rhodesian commando raid into the Zambian capital of Lusaka Friday was aimed exclusively at guerrilla military targets and that it was not an attempt to assassinate black nationalist leader Joshua Nkomo.

Walls seemed eager to stress that the sole purpose of the attack early Friday morning on Nkomo's residence was to knock out his "personal command post."

"There is no question of us having been striking at Nkomo," he said. "I don't mean to be boastful, but I would like to suggest that our record shows that if we wanted to kill Nkomo we would have done so," he added later.

Ten of Nkomo's guards were killed in the attack and his home was largely destroyed by bazooka fire and explosive charges set off inside. The nationalist leader either escaped or was sleeping elsewhere and went unharmed.

Walls refused to say what Rhodesian commandos would have done had they found and captured Nkomo at his home, but suggested they knew that he was staying elsewhere in Lusaka.

Friday, Bishop Abel Muzorewa, Rhodesia's likely first black prime minister after next week's elections, made it clear he would not support a policy of attempting to assassinate other Rhodesian black nationalist leaders and told reporters he was unaware the raid on Nkomo's home in Lusaka was being planned.

Walls seemed to be responding to the bishop's apparent concern that the attack might result in guerrilla reprisals against the three black leaders of the Salisbury government if viewed as attempt to kill Nkomo.

The general would give no details of how the latest raids into Zambia and Botswana were executed or what the results had been.

But he said only Nkomo's command post and the Zambian-sponsored Liberation Center had been hit inside Lusaka. In Botswana, only the guerrilla military headquarters in Francistown and the ferry at the Zambian-Botswanan border were hit, he said. The only casualties on the Rhodesian side were three injured, he added.

He also refused to provide any concrete evidence of Rhodesian allegations of growing Soviet involvment in Nkomo's army. But he said his intelligence reports showed the Soviets were helping with the development of Nkomo's forces, planning strategy and even debriefing returning guerrillas.

"The Russians have got themselves involved in the control and direction of the Zambawa People's Revolutionary Army (ZIPRA), he said, referring to Nkomo's army.

Walls derided Western fears that the Rhodesian attacks into neighboring African countries might trigger Cuba into sending troops to help the guerrillas and thus escalate the war.

"I've always said that the Cuban menace, the Cuban myth is just that. It's a myth. They could help but I doubt they are going to do much more physical helping because if they do, it will be the end of the Cuban myth, I don't think their Russian masters can afford to allow that to happen," he said.

The gray-haired general appeared extremely confident that his vastly expanded security forces could provide an effective "blanket of security" for all Africans wishing to go to the polls next week despite guerrillas threats to disrupt the elections.

He said the best military defense was always to go on the offensive, apparently indicating the Army intended to take advantage of the current full mobilization of police and military reserves to take the war to the guerrillas' stronghold both inside and outside the country. This could explain the large number of guerrillas reported killed in the past 48 hours.

Shortly after his press conference, correspondents watched two Rhodesian Canberra bombers flying over the capital as they returned from yet another raid into Zambia. A brief military communique said they had bombed a guerrilla camp at Mulungushi, 80 miles north of Lusaka.