The deadline for release of several political prisoners in return for the lives of six American, British and Australian hostages held by dissidents in southwestern Zimbabwe passed this afternoon without any indication that any of the captives had been killed.

Rather than releasing detainees, the government charged in court that 17 members of Joshua Nkomo's opposition party, including a member of Parliament, planned and executed an attack last month on the official residence of Prime Minister Robert Mugabe.

A spate of unconfirmed reports this morning that bodies of three hostages had been found created an air of tension in the capital, which is more than 300 miles from the hostage operation.

The three embassies representing the hostages were deeply concerned until early this afternoon, when Ian Findlay, the undersecretary at the Ministry of Information, denied the reports, telling reporters, "No graves or bodies have been found."

Until then numerous officials and diplomats had been unable to confirm or deny reports by all four major Western international news agencies, citing unidentified sources, that three bodies had been found. As the rumor spread it was embellished with details: that the dead were two Britons and an Australian and that pictures of the bodies had been taken.

In denying the reports, Findlay explained that "clothing was found in a village in the possession of an individual who on questioning said he had been involved in the burying of three people. He was told to indicate the position of the three graves but was unable to do so."

One possible explanation was that the poor communications between the regional capital of Bulawayo and the 1,500-man task force searching for the hostages and dissidents formerly loyal to Nkomo led to a garbled report. There are no telephones in the vast scrubland area north of Bulawayo where the search is being conducted, and all communications are by radio.

It is also possible, but less likely, that the dissidents, who claim the government is discriminating against Nkomo and his minority Ndebele tribe, used the villager in a "disinformation" campaign similar to those used by such terrorist groups as Italy's Red Brigades.

A Western diplomat, in a pessimistic vein, noted that it was also possible that the villager was telling the truth but then became scared when pressed by the troops.

The two Americans, two Britons and two Australians were seized by 10 to 14 dissidents last Friday about 50 miles north of Bulawayo on the road to Victoria Falls. The large military force searching for them has reported no progress in recent days.

In fact, Findlay's denial was the first official government statement on the hostages since a terse announcement that the hostages had been taken.

The British High Commission said Friday that three young British tourists had not been heard from since they left the capital two weeks ago on a tour of the eastern highlands, Reuter reported. That area generally has not been affected by the recent unrest in the southern part of the country, where the six missing tourists were abducted. There is no suggestion at this point that the young Britons have been similarly abducted.

There is no indication that the government would consider releasing the prisoners, including former guerrilla military leaders Lookout Masuku and Dumiso Dabengwa and member of Parliament Vote Moyo. Masuku and Dabengwa were charged with treason yesterday and Moyo was among the 17 Nkomo followers charged today with involvement in the attack on Mugabe's house.

Mugabe has charged Nkomo's Zimbabwe African People's Union with responsibility for the kidnaping and warned of harsh retaliation.

In an interview tonight with the Chronicle newspaper in Bulawayo, Nkomo denied that his party had anything to do with the kidnaping and said dissidence was "a national problem, not a ZAPU problem."

He appealed to the dissidents to release the hostages but said the former guerrillas were "completely outside our control and knowledge."