Prime Minister Robert Mugabe today accused the party of his political rival Joshua Nkomo of responsibility for the kidnaping of six foreign tourists and warned the party leaders that they would be in "serious jeopardy" unless they "desist from their clandestine organization of banditry."

"The swords are drawn, and it will be a luta continua to the finish," Mugabe told Parliament, using a Portuguese-language revolutionary cry meaning "constant battle."

"I appeal to the leadership of Nkomo's party to do all it can to retrieve the hostages," Mugabe said as Assemblyman Nkomo sat silently nearby.

Mugabe's speech was his harshest attack on Nkomo's Zimbabwe African People's Union (ZAPU) since he fired his former partner from the Cabinet in February.

A task force of more than 1,500 troops and police have been unable to track down the kidnapers and their hostages, including two Americans, captured last Friday.

The dissidents have threatened to start killing the hostages Friday unless the government releases from prison key Nkomo supporters, ceases attacks on the party and returns its confiscated properties.

Another incident, on Sunday, put in doubt the government's ability to maintain security when a mysterious attack on the key Thornhill Base in the center of the country destroyed a quarter of Zimbabwe's Air Force planes. Eleven men, most of them whites, were detained yesterday in connection with the attack on the base, informed sources said.

In addition, the government brought to court today two of the key prisoners the dissidents want released, ex-guerrilla leaders Dumiso Dabengwa and Lookout Masuku, and charged them with treason. Five other ZAPU members were similarly charged.

Mugabe made it clear that, despite the seizing of the hostages, he would not back away from a confrontation with Nkomo's party in its stronghold of Matebeleland in southwestern Zimbabwe, where dissident activity has resulted in at least 30 deaths in the last few months.

"We shall never ever allow a gang of criminal bandits and the party which sponsors their criminality to usurp sovereignty over the people," he said. "Accordingly, I shall be invoking extremely harsh and short-shrift measures to administer shock treatment to these harmful pests and their deceitful mentors.

"The bandits are operating on instructions from a number of ZAPU leaders. These men are ZAPU. The weapons are from ZAPU . . . ZAPU alone has created the bandits and ZAPU alone must unmake them."

Nkomo did not respond in Parliament and declined to come to the phone tonight to answer a reporter's questions.

Mugabe, in throwing down the gauntlet, threatened to intensify the tribal animosity that has been on the upsurge since Nkomo was deposed for secreting arms caches. Mugabe is from the Shona tribe, which makes up about 80 percent of the country's population. Nkomo is the leader of the minority Ndebeles, centered in Matabeleland where the kidnaping occurred.

Tribal animosity was usually buried during the seven-year struggle to overthrow white-minority rule in this southern African country, then known as Rhodesia. The resurgence comes amid increasing problems for Mugabe's government, which was elected in the euphoria of independence 2 1/2 years ago.

The sabotage at the air base involved plastic explosives placed in the planes' engine cowlings. Destroyed or damaged were 12 jet fighters and a helicopter, including four new Hawk jets just delivered from Britain this month at a cost of about $35 million. It is believed that three men cut their way through a fence around the base and placed the explosives in the planes in widely separated areas of the base, on the runway and in hangars.

It is understood that several of the 11 detainees are officers or former officers in the Air Force, but details are sparse. The government has been silent on the attack since an announcement that "entrance was gained" into the base, that "a number of aircraft were damaged by sabotage" and that "an inquiry is being conducted."

Attacks last year on an Army base and on Mugabe's party headquarters were almost immediately blamed on neighboring white-ruled South Africa or on white malcontents, but this time the government has refrained from making such charges.

It is generally believed, however, that there is no connection between the attack on the air base and the kidnaping. Most observers say the sabotage was too sophisticated to have been carried out by the dissidents and required intimate knowledge of the base.

After optimism early this week that the Army was closing in on the kidnapers north of Bulawayo, capital of Matabeleland, it appears that troops have now lost track of the hostages. It is believed that the dissidents have broken up into three groups to make detection more difficult.

The Army is using planes, helicopters, small tanks and armored personnel carriers to search the arid bush terrain. Two of the captives are British and the other two are Australian. Britain has flown in five marksmen from the elite Special Air Services to help capture the kidnapers.