Dissidents involved in the kidnaping last July of six foreign tourists, including two Americans, have said in a note that the hostages are still alive but may be killed, a government spokesman said today.

The spokesman said six armed dissidents kidnaped a white farmer in southwestern Zimbabwe yesterday and left a message warning that the six foreign captives and the farmer would be killed by the end of the month unless the government released two imprisoned former guerrilla leaders on trial for treason.

The message was released by the government news agency. It was the first time the government has publicized an indication, allegedly from the dissidents, that the two Americans, two Britons and two Australians were still alive.

The hostages have been the object of a manhunt by the Army and police since their abduction, and the government and their parents have offered rewards. The parents have used full-page newspaper ads and radio broadcasts to seek information about their sons.

There have been unofficial reports of communication, but until today the government had not disclosed any information about messages from the kidnapers, who are accused of supporting self-exiled opposition leader Joshua Nkomo.

Emerson Munangagwa, the minister in charge of security, said in a television interview two months ago that he believed five of the six were alive based on sketchy reports from villagers.

The two abducted Americans are Kevin Ellis of Seattle and Brett Baldwin of Walnut Creek, Calif.

The tourists' embassies were notified today, but a diplomat from one of them said it was not yet known "whether somebody was operating opportunistically or whether the message was for real."

The new note demanded only the release of Dumiso Dabengwa and Lookout Masuku, Nkomo's two top military officials during the guerrilla war for independence, the government news agency said. The original demand last July also called for an end to government attacks on Nkomo and the return of farms owned by his party that were seized last year after buried weapons were found on the property.

The trial of Dabengwa and Masuku and five others on treason charges resumed in Harare today after a three-week recess.

Yesterday's abduction of farmer Dyre Smith, southwest of Bulawayo, shows that the dissidents are still active despite an Army sweep in the vast area where the Ndebele tribe, a minority in the country, is dominant.