It was a night of horror that one Red Cross official called "the worst of the war" as renegade National Guard soldiers fought, not for their country, but for their lives in small groups throughout the city.

No one had told them the war was over.

Then, shortly before dawn, Managua woke up to the sound of music - rebel hymns and songs of triumph of pouring from the national radio that only Wednesday had warned of death and destruction at the hand of the "communist mercenaries."

"Be calm," the radio told them. "Act with maturity. The moment is coming when all Nicaraguans, regardless of their beliefs, can go into the streets together and rejoice."

To the National Guard holdouts, the radio said, "You have no reason to fight. Somoza has gone. [Interim president] Urcuyo has gone. [National Guard director] Mejia and the entire command have gone. There is nothing to defend. Don't lose your life uselessly. Go to the nearst church, the nearest Red Cross. Surrender your arms."

Early this morning, Sandinista guerrillas surrounded "the bunker," the office and residence of former president Anastasio Somoza inside the National Guard headquarters complex.

Rifles ready, they moved cautiously through the gates, expecting soldiers to jump out from behind a row of empty Mercedes cars and armored vehicles. Instead, the only living thing they found inside was a half-grown German shepherd, abandoned by its master and wandering forlornly.

For a few moments, the guerrillas stood in confusion, and it soon became apparent that they did not know which of the many doors in the complex led to the inner sanctum that had been the focus of their hatred for so many years.

A foreign photographer recording their entrance had to direct the Sandinistas to Somoza's office.

By afternoon, Sandista leaders "Comandante Marcos" and "Comandante Oscar" had set up their headquarters inside.

An hour before the Sandinistas arrived at the bunker, a group of journalists had gone through Somoza's quarters and found them as though their occupant had just gone out for a cup of coffee.

Papers were strewn across the reception desk where only hours before National Guard soldiers had loaded their guns. Behind the office was the small apartment where Somoza spent his last weeks in office.

Across an unmade bed lay a military fatigue uniform with the name Somoza across the pocket. Inside the closets hung rows of dress uniforms, each with the five stars of the "Supreme National Guard Commander" on their shoulders.

When the Sandinistas finally came in, they ran about pocketing souvenirs. Spying a youthful portrait of Somoza on the wall, they ripped it down, tore it to shreds and one man urinated on it.

The celebration in Managua began slowly, but it soon gathered momentum as residents realized the fighting was really finished.

Crying and laughing, people ran for their cars and tore through the streets with horns screaming. Others stoods on the curbs or wandered the streets in groups, not quite knowing what to do. It seemed as though they could not grin enough, could not wave their arms, fingers spread in a V for victory, high enough.

As if out of the woodwork, thousands of armed young men and women appeared. Members of the "popular militia," the youthful Sandinista supporters in Managua's poor barrios, had launched # impromptu parades through the city, hanging out of the windows and sitting on the roofs of commandeered pickup trucks, buses and National Guard vehicles.

At the sports stadium named for Somoza's fahter, crowds pulled down an equestrian statue of the dynasty's founder and ripped the letters of his name from the wall.

With a sound like a thousand Fourths of July, shots fired in the air rang throughout the city. By noon, the young rebels filled National Guard headquarters and were helping themselves despite guerrilla orders to maintain discipline.

At Red Cross centers and churches, hundreds of National Guary soldiers lined up to seek refuge. Most were in the civilian clothes they had worn under the uniforms that this morning littered the streets.

Inside the refugee centers, the soldiers appeared more shell-shocked and confused than frightened. They were processed by Red Cross workers, who took down their names and gave them numbers and told them they would be sent to temporary refuge in an embassy or other center until their futures were straightened out. Neither guerrillas nor guns were in evidence.

One young guerrilla assigned to guard the national telecommunications center stood with a smile on his face and a large orange beach hat perched incongruously on his head.

"There's nothing to worry about," he told anxious motorists with a reference to the Sandinista slogan, "A free country, or death." "This is a free country, with no more death." CAPTION: Picture, Sandinista priest Ernesto Cardinal, left, looks on as junta member Alfonso Robelo, right, arrives in Leon. UPI