A high Zimbabwean security official has given the first positive indication that his government believes some of the six foreign tourists, including two Americans, kidnaped six months ago in southwestern Zimbabwe still may be alive.

Emmerson Munangagwa, the minister of state in charge of security affairs in Prime Minister Robert Mugabe's government, said in a television interview broadcast last night that "at least five are possibly still alive. The sixth, I have doubts. We believe the five are still alive."

In a telephone interview today he said that his remarks were based on several reports in November of sightings in the area of two separate groups containing a total of five whites. The Zimbabwe Television program was taped for broadcast in late November, he said, and there have been no sightings since then.

"The somewhat positive reports" of sightings were "consistent," he said, but he would not say where the men had been seen. There were three whites in one group and two in the other, leading him to believe that the sixth captive was no longer alive.

He declined to give any other details, including any information on which of the six may be dead.

Munangagwa's remarks were the first by a senior government official on the possible fate of the two Americans, two Britons and two Australians since they were kidnaped on the main highway from Victoria Falls to Bulawayo in late July.

The kidnapers, former guerrillas loyal to opposition leader Joshua Nkomo, demanded the return of 11 farms owned by Nkomo's party and the release from prison of a number of Nkomo supporters. They were arrested and the farms were seized early last year after large weapons caches were discovered and Nkomo, an ally of Mugabe in a guerrilla war for black rule, was accused of plotting a coup. Nkomo has denied any association with the dissidents.

The government has refused to negotiate on any of the demands and instead is scheduled next week to bring to trial on treason charges the two main prisoners, Dumiso Dabengwa and Lookout Masuku, former leaders of Nkomo's guerrilla army.

The two Americans are Kevin Ellis, 24, of Seattle, and Brett Baldwin, 23, of Walnut Creek, Calif. They were on an overland safari through Africa.

The lack of any public information has led to a widespread belief in the country that the men are dead, but government troops and police have continued searching the vast bushland area bordering on the west with Botswana. A reward of $11,000 has been offered, and the government radio has broadcast appeals from the families of the men seeking their release.

Western diplomats in touch with security officials say very little information is coming out of the area. Some analysts and white farmers in the Nkomo stronghold known as Matebeleland have accused the government of alienating the local Ndebele tribe by favoring Mugabe's majority Shona tribe and thus helping the dissidents gain support.

"People in this part of the world have the ability to snatch people and keep them out of sight for a long time," said a diplomat who believes the captives are still alive. "There are also probably a couple hundred mine shafts in the area where bodies could be dumped and never found," he added, "but somebody, somewhere will eventually talk."

Meanwhile, government forces searched for two Zimbabweans kidnaped on New Year's Eve from a mine near Bulawayo in the latest wave of dissident violence in Matabeleland. The body of the third captive, an elderly white man, was found beheaded.

Thirty miles to the west, also on New Year's Eve, dissidents attacked a farm vehicle carrying five whites, including two children, and a security guard and killed all six.

On Christmas Eve three blacks were killed when dissidents attacked and burned two buses and cars on the main Bulawayo-to-Harare highway and also shot at a train.

No arrests have been announced in any of the cases, but Mugabe ordered extra troops into Matabeleland after the Dec. 24 slayings and denounced "such perpetrators of evil" in a New Year's Eve broadcast.

Cephas Msipa, minister of water resources and development, said yesterday that dissidents had destroyed more than $2 million worth of water development equipment in the drought-stricken Tsholotsho area in the region where the foreign tourists were seized.

In his televised interview Munangagwa blamed South Africa for supporting much of the violence in the country.

He accused Pretoria of "continuously sending armed bandits into the country to commit acts of sabotage against vital economic installations" and also said South African troops "violate our borders day in and day out." There has been at least one clash against South African troops inside Zimbabwe in which three South Africans were killed.

He charged South Africa with setting up a "Matabele Brigade" among Ndebeles in South Africa. In Zimbabwe's most detailed accusations against South Africa, the minister said the "brigade" was trained at four different camps in northern Transvaal under the command of a Colonel Breytenbach.

Munangagwa said the unit intended to operate inside Zimbabwe in the same way that South African-backed rebel groups have destabilized Marxist governments in Mozambique and Angola.