MANAGUA, NICARAGUA, SEPT. 12 -- Nicaragua's top human rights activist and a leading lawyer, both released from jail this week, said the government held them for 25 days to discourage opposition groups from becoming more outspoken as the deadline for a regional peace pact approaches.

Lino Hernandez, head of the only independent human rights commission here, and Alberto Saborio, president of the Nicaraguan Bar Association, were released Tuesday to visiting Sen. Tom Harkin (D-Iowa), five days before they would have completed a 30-day sentence for disturbing the peace.

In separate interviews, Hernandez and Saborio said they were not mistreated by their police captors, but added that they believed their detention was purposely prolonged as a warning to the opposition by the leftist Sandinista government.

They were picked up Aug. 15, when police used attack dogs and electric cattle prods to break up an opposition demonstration that was planned as the first test of new freedoms promised under a pact signed a week earlier by the five Central American presidents.

A scratchy growth of beard still covered Hernandez's sunken cheeks. Both men said they were nearly 20 pounds thinner after they went on a two-week hunger strike in cells they described as stinking and bare. Unlike other political prisoners, they were held in a neighborhood police station in a cell block used for criminals, they said. They were never interrogated or taken to the isolation cells of the state security police, they said.

Although neither man spoke at the August rally, they were singled out as the gathering of 300 was dispersed by plainclothes police who beat them with rubber hoses and electric prods, they said.

"They went after us to frighten people into paralysis, so when the peace pact takes effect they won't try to exercise their rights," Saborio charged. The accord calls for an amnesty, a cease-fire and full democratic rights to be restored simultaneously in all five Central American countries on Nov. 7.

They said that a few days after they were jailed, police chief Doris Tijerino visited them to urge them to appeal a summary sentence that a Sandinista judge had handed down the day of their arrest. They said they, and the police guarding them, expected they would be freed shortly.

But the police abruptly received "higher orders," they said they were told, countermanding the expected release. That decision fueled speculation that differences had arisen between President Daniel Ortega, who signed the peace pact, and Interior Minister Tomas Borge, a more uncompromising Marxist who is charge of the political police.

The release to Harkin was made to appear spontaneous but apparently was decided well ahead of time. Three days beforehand, the two lawyers were moved to clean cells and encouraged to eat and clean up, Saborio said.

Harkin got a surprise from Saborio, whom he took directly from jail to lunch at the posh U.S. Embassy residence. Saborio said he told Harkin, a liberal opponent of U.S. aid to the rebels fighting to oust the Sandinista government: "When a government tries to enslave its people, there comes an hour when they have no choice but to take up arms. For Nicaragua, that hour has come."

Hernandez predicted that the government's compliance with the peace plan will be "partial."

"They can reopen La Prensa {an opposition daily} and the Catholic Radio, but the underlying repressive legal apparatus will remain intact. At any moment they can roll us right back to zero," he said.

For Hernandez, the litmus test of the peace plan will be if the government releases all its political prisoners, estimated to number more than 5,000.

More than 1,500 Nicaraguans are in jail awaiting trials or sentencing on suspicion of collaborating with the rebels, known as counterrevolutionaries or contras. Many of these are held incommunicado in state security prisons, Hernandez said.

The accord's text does not require the region's governments to release political prisoners, but opposition groups and leaders in the region have interpreted the peace plan's call for general amnesty to apply also to those jailed for political crimes.

A debate is raging in the Sandinista-controlled press over which prisoners can be said to have committed "crimes against the state" and therefore should be ineligible for amnesty.

"They can open La Prensa, and they can close it. But they can't round up all those prisoners again once they let them go," Hernandez said.