ROME (AP) _ Six convicts holding 21 hostages in a prison infirmary on the island of Elba on Saturday released a 65-year-old inmate with heart trouble.

One hostage, prison director Cosimo Giordano, was interviewed Saturday in a taped, nationwide broadcast.

Inmate Claudio Rubini was released after he apparently became hysterical and began screaming at the mutinous inmates, officials said. Rubini was one of those being treated in the infirmary when it was seized Tuesday by six inmates armed with guns, knives and explosives.

State-run RAI television and the ANSA news agency quoted Rubini as saying the situation inside the prison was ''dramatic, worse than you can imagine.''

''The air was made unbreathable by the fumes from alcohol, gasoline,'' he said. Bottles of the liquids were placed around the infirmary.

''We were constantly afraid we would be blown up,'' ANSA quoted Rubini as saying. Neither RAI nor ANSA said where Rubini made his comments.

Justice Minister Giuliano Vassalli flew from Rome to the island, where he met with negotiators and with relatives of the hostages.

Ernesto Olivero, the director of a private social service agency that works with prisoners, also arrived on the island 125 miles northwest of Rome to help with negotiations.

In an interview with RAI, Olivero said he hoped to speak with the inmates Sunday.

Giordano said in a taped telephone call broadcast by RAI that the six rebels formed an ''extremely compact'' group that showed no sign of division.

He said seven inmates who were in or near the infirmary when the revolt erupted had nothing to do with the uprising and were being treated like the 21 prison staff members taken hostage.

Five of the rebellious inmates are serving life sentences on kidnapping and murder charges.

The prison director said that there was no leader among the six. ''They are all of the same importance,'' he said.

It had been presumed that convicted right-wing terrorist Mario Tuti, 40, was the ringleader since he was the one communicating with officials by telephone. RAI said negotiators were now communicating with other mutinous convicts.

Authorities on Friday refused the inmates' demand for a helicopter in which to flee the island with two hostages.