Along side the dirt road leading to Modelo prison, a small market has sprung up where relatives of the more than 3,000 former National Guardsmen buy eggs, broiled chicken, fruit and bread to send to their loved ones inside.

Each day, up to 100 relatives, mostly women, have gathered at the prison gates, hoping that the Sandinista soldiers in charge of the overcrowded but relatively comfortable complex would let them visit their jailed husbands, fathers or sons.

The ruling junta began filling the prison Friday after placing under arrest the thousands of Guardsmen and officials of Anastasio Somoza's ousted government who had taken refuge in Red Cross-operated camps.

So far, no more than a handful of the families at the gate have been allowed to visit within. Instead, they wait under the hot summer sun, anxiously asking the few doctors, journalists and Red Cross workers who enter and leave each morning and afternoon if they have word of Jose Garcia or Adolfo Munoz or some other member of the defeated guard.

Modelo prison here in Tipitapa, about 15 miles from Managua, has become the Sandinistas' main detention center just as it was the main prison under Somoza. Interior Minister Tomas Borge changed the Guardsmen's status from refugees to prisoners of war after charging they had staged sniper attacks from the refugee centers -- a charge greeted with skepticism by Red Cross officials.

The women outside want to know if the food packages they send in are being delivered, if the prisoners are being mistreated, if there is any indication when a promised list of all those being held will be made public. Journalists who enter the complex are jeered at by some of the waiting relatives: Tell the truth! Tell the trith!"

After a visit of three hours today and long unmonitored conversations with a dozen prisoners, the truth seems to be what leaders of the Sandinistas National Liberation Front say it is.

"We have nothing to hide," Interior Minister Borge said the other night when he gave the order to open Modelo prison to any foreign journalists who wanted to see for themselves.

The prison, designed to house about 1,000 prisoners, is overcrowded. The International Red Cross has so far been able to arrange enough food to feed the 3,000 men and boys inside only once a day. The prisoners complain about not seeking their relatives and, in some cases, say they have been unable even to send word that they are there.

But in conversations in the cell block, away from sandinista guards, not one prisoner alleged torture or mistreatment. Indeed, most of the prisoners -- who only three weeks ago were fighting one of the bloodiest and most brutal civil wars in recent history -- had only praise for the treatment they have received from the Sandinistas.

"The boys treat us well," said Jose Amador Reyes, 62, a retired member of the National Guard, during an interview in his cell block on the first floor of the two-story prison. "I'm not afraid. The only problem is the food and that my family doesn't know i'm here."

Amador, like several others interviewed at random, said he didn't know why he had been jailed. He said he retired from the National Guard 13 years ago and was working as an immigration officer at Managua's airport. He said he was arrested when he reported to work after the war ended last week.

Marcio Marinea Ortiz, 21, the dark and bearded young Sandinista partisan who was serving today as the prison's cheif security officer, said that unfortunately there are cases of persons who may be innocent of war crimes being swept up either during or after the war.

Marinea, who walks among his prisoners without fear and who seems to have their respect, said committees appointed to investigate each of the prisoners already have begun work. "Those who committed crimes will be punished. But those who did not will be allowed to leave as soon as possible.

"We are not seeking retribution. We have not beaten or tortured anyone," he said. "We want out revolution to be an example for all of Latin America."

Marinea said that he and the top Sandinista leadership know that how they treat their prisoners will be important in the way their revolution is judged both inside Nicaragua and abroad. He expressed determination that Modelo prison be the model pison its name implies.

Prisoners are given food that is varied and well prepared -- but served only once a day. A doctor is usually on duty and the small clinic was busy treating ailments this morning. Prisoners are allowed complete freedom to play cards, listen to their radios and exercise in the long cellblock corridors.

Each cell has a shower and the prisoners appeared to be clean nd recently shaven. Jose Alviro Tijirino, 31, a former sergeant in the National Guard, said there were a few frightening moments after he was brought to Modelo a week ago, but that since "Commandante Marcio" took over, things have greatly improved.

Asked if he or other members of the guard would take up arms again on Somoza's behalf should the former dictator attempt to overthrow the Sandinistas, Tijirino said he never again wanted to be involved in a war -- on Somoza's behalf or anyone else's. CAPTION: Picture, A 17-year-old Sandinista stands watch at the Modelo prison housing National Guardsmen 15 miles from Managua. UPI