OAKDALE, LA., NOV. 26 -- Cuban inmates who controlled the federal detention center here for a sixth day apparently reached an agreement tonight with a federal negotiator to release their remaining 27 hostages. One hostage, corrections officer William Hoffpauir Jr., was freed late last night.

At the Atlanta Federal Penitentiary, Cuban inmates in the fourth day of a siege met for 90 minutes tonight with three prominent Cuban Americans, then rejected a proposal that they release 50 of their 94 hostages.

Rioting broke out here Saturday and spread to the Atlanta prison Monday after the United States revived a diplomatic agreement to deport 2,500 of the 125,000 Cuban refugees who arrived in the 1980 Mariel boatlifts. Attorney General Edwin Meese III offered a moratorium on such deportations, and case-by-case reviews of each inmate's immigration status, "in the expectation" that the uprisings would end.

In a videotape made by pool reporters admitted to the detention center here last night, an unidentified federal negotiator said a typed agreement would be signed by the inmates' four representatives at 1 p.m. Friday, "then they will release the other 27 hostages."

Details of the agreement were not released. The negotiator said it would take effect when all the hostages were freed.

On the tape, the negotiator shook hands with inmate Manuel Monzon and said, "We have a deal." It appeared that Hoffpauir, seen on the videotape walking unaided from the center, was released to seal the agreement. J.D. Williams, a U.S. Bureau of Prisons official, said he "seemed to be in excellent spirits."

Among the Cuban-American mediators who entered the prison in Atlanta was businessman Jorge Mas Canosa, President Reagan's Florida campaign manager in 1984 and head of the Cuban-American National Foundation, which operates Radio Marti's U.S.-funded broadcasts into Cuba.

The others were poet-writer Armando Valladeres and Robert Martin Perez, both former political prisoners in Cuba. The three entered the prison with an FBI negotiator and spoke with three Cuban inmates who described themselves as spokesmen for an inmate "commission."

Justice Department spokesman Thomas M. Stewart said the spokesmen for the inmates took the proposal back to the inmates, who voted against releasing 50 hostages but considered releasing three tonight. Three hostages were moved to the prison hospital before the inmates decided against releasing any hostages.

Officials released no details of their deliberations. But Stewart said later, "We're well beyond square one. They're talking."

Weldon L. Kennedy, special agent in charge of the FBI's Atlanta office, said the selection of the spokesmen indicated that the inmates there, divided for three days into at least 10 factions, are beginning to get organized.

In a taped interview with an Atlanta television crew inside the prison, Kennedy said they were "representatives of a commission of individuals who allegedly have emerged as a leadership group of the detainees."

Earlier in the day, Stewart had described the negotiations there as "flat and uneventful," saying the inmates "haven't gotten their act together to negotiate as a unit."

It was unclear, according to reporters who participated in a news media pool that entered the prison last night, who initiated the proposal to free some of the hostages. According to Kennedy, the three mediators approached the U.S. Bureau of Prisons in Washington to offer their services.

Kennedy, who has shared the prison command center with the warden, said in the interview that there are other signs of increasing organization inside the prison: "A lot of trash and debris is being cleaned up. There appears to be regular food service."

Ozell Sutton, a regional Justice Department official in Atlanta, said some of today's earlier negotiations there took place in neutral territory inside the prison where inmates and officials could speak to each other from a distance. Most of the intermittent talks were conducted on the telephone.

Negotiations with the four inmates, among more than 1,000 Cuban detainees at Oakdale, were set for 1 p.m. today, but were unexpectedly delayed. Sen. John B. Breaux (D-La.) said later that the inmates were considering a counterproposal to seven undisclosed demands made by the inmates during three hours of talks Wednesday night.

Mark Sheehan, the Justice Department's spokesman in Oakdale, had said federal officials here were "mildly encouraged" because the four Cubans appeared to have the backing of most inmates.

The Rev. Roy Bourgeois, a former inmate at the detention center, said Hoffpauir, the freed hostage, "got along well with the inmates. He wasn't a hard-ass." Monzon, he said, was well-liked.

At a midday news conference in Washington, U.S. Bureau of Prisons Director J. Michael Quinlan said he was "very encouraged" that the Oakdale negotiations were "getting to a point where there might be a resolution in sight." He said he hoped an agreement in Oakdale might hasten a resolution in Atlanta.

Of the 1,397 Cubans and 194 Americans normally housed at the Atlanta prison, officials now say that 171 Americans and 247 Cubans have surrendered and been transferred to other federal detention centers. Stewart said they generally turned themselves in by "approaching a guard tower and saying they want to get out."

"The opportunities to leave are always present," Stewart said this afternoon. "We have no reason to believe any prisoner is being held against his will, but some are more lukewarm about what is going on than others."

Several buses waited today behind the Atlanta prison, which covers about 24 square city blocks. The ranks of inmate and hostage families waiting outside the 25-foot-high walls thinned as the siege wore on under a warm, heavy rain. Some gathered in a nearby tent to eat donated turkey dinners.

Quinlan and Attorney General Edwin Meese III made telephone calls to hostage families today, and relatives gathered in an Oakdale church building to hear a noon message from Meese before church volunteers served them turkey, ham and Cajun gumbo.

At his Washington briefing today, Quinlan said the hostages at both facilities "are reported to be safe. Their safety continues to be our No. 1 concern."

Officials in Oakdale would not describe the conditions set by inmates for their hostages' release. Rep. Clyde C. Holloway (R-La.) said today that one of the demands was for food and water; Quinlan said food and water had not been provided at either facility.

Patsy Grimes, with several other hostage relatives here, said she prayed for the inmates as well as the hostages and bore no ill will toward the Cubans for taking over the detention center.

"I really sympathize with them," she said. "That was the only way they could communicate their feelings."

Grimes said her husband, Michael, a prison guard, considered several inmates his friends and had been learning Spanish from them. "I do know that he was sympathetic to them. I don't know what he's feeling now," she said.

Grimes said she felt confident that her husband is safe because she recently saw a photograph of him taken by the inmates. "He looked like he normally does to me," she said. "He was smiling."

Other hostage relatives were not as confident. Ernestine Pickens, whose 27-year-old son Andre White is a guard at the detention center, said, "My Thanksgiving day will begin when my son comes home."

Manuel Martinez, the chaplain at the Oakdale detention center, said he was praying for "divine intervention" to assure freedom for the hostages and help for the Cuban inmates. "You're torn apart," he said. "You feel for all the people involved."

Gail McJunkin, whose brother, Leon Smith, is a hostage, said federal authorities had tried to deliver Thanksgiving meals to the hostages Wednesday evening but that the food was turned back. She said the inmates apparently feared that it might have been poisoned, and "they didn't want to be blamed for anything that might happen to the hostages."

Not all of the Cuban inmates here and in Atlanta are among the Marielitos to be deported. The list includes refugees who committed crimes in Cuba, were mental patients in Cuba or have served sentences for crimes committed in the United States and lost their eligibilty to remain.

But the rebelling inmates at both facilities have indicated that they had trouble believing the offer of a moratorium.

Reporters allowed to go near the Oakdale center today said inmates had put up a sign saying, "U.S. Government, Please Allow Us to Speak to Someone We Can Trust Who Understands Our Lang{uage}."

A spokesman for an Atlanta-based organization that has worked with Cuban prisoners for about three years urged federal authorities to call in Hispanic leaders familiar to the inmates.

"We need someone who can get through to them," said Steven Donziger of the Coalition to Support Cuban Detainees.

One inmate was taken out of the prison here late this afternoon with what officials said was a knife wound. A second inmate was taken out suffering from a drug overdose. More than 30 people, inmates and guards, were injured in the initial rioting. One inmate was killed early in the Atlanta uprising, and 12 inmates and guards were injured.

The Defense Department dispatched about 100 special operations advisers, antiterrorism specialists, to the prison there on Wednesday.

Staff writer Molly Moore in Washington and Morris S. Thompson in Atlanta contributed to this report.