PANAMA CITY, Panama -- "When we saw Jimmy Carter's letter to Somoza, praising him, we decided that the hour to strike had arrived," Eden Pastora Gomez said quietly, leaning back in the corner of the couch where he sat with his fellow guerrilla leaders.

Pastora, better known as "Commander Zero," was the chief of the leftist revolutionary Nicaraguan guerrilla commandos -- 24 men and one woman -- who on Aug. 22 captured the National Palace in Managua, the capital of Nicaragua, in an extraordinarily daring raid. For 68 hours, the commando unit held the palace, with over 2,000 persons inside, until its demands were met by the government of President Anastasio Somoza Debayle.

Had the demands been refused, "Commander Zero" told me,, the guerrillas were determined to execute, one by one, at half-hour intervals, the 65 hostages considered members of the Somoza establishment who were in the throng trapped in the palace, the seat of the Nicaraguan congress. The first execution, in fact, was three hours away when the Somoza dictatorship agreed to the conditions of the revolutionaries.

The attack, in the judgment of some experts on Nicaraguan affairs, has triggered what may be the approaching collapse of the regime. At the same time, it has underlined the importance of the highly organized and ideologically motivated revolutionary movement in terms of future developments in that central American Republic. If the Nicaraguan army should disintegrate, the guerrillas would be the only armed force on the scene.

While the movement's leaders indicated that they would be prepared to cooperate with "democratic" groups in Nicaragua in a post-Somoza transition period they envision, their ultimate ambition is to assume power alone.

If they come to power, they said, they would establish a revolutionary state -- "Commander Zero" exclaimed at one point that "there are only two solutions in Nicaragua: the revolutionary way and the counterrevolutionary way" -- that would expropriate all Somoza property, nationalize natural resources and implant social justice along with the establishment of a "popular and Democratic army."

The guerrillas left no doubt about their admiration for the Cuban revolution, whose influence is powerful within the movement, and their bitterness toward the United States for its long-standing backing of Gen. Somoza, whose father was installed in the 1920s with instrumental American support. The Nicaraguan revolutionaries, consequently, pose a major political problem for the Carter administration in terms of the stability of Central America -- where rebel movements also exist in El Salvador, Guatemala and Honduras -- unless a formula can be devised to encourage the Nicaraguan guerrillas to go along with a centrist compromise, a doubtful proposition.

Last Wednesday, "Commander Zero," his two principal commando associates and Tomas Borge Martinez, who has emerged as the political and ideological leader of the Nicaraguan rebel movement that calls itself the "Sandinist Front of National Liberation" (FSLN), agreed to a lengthy interview to describe their goals and, for the first time, to narrate in detail how the Managua raid was planned and carried out.

The four-hour interview took place in a large room at the barracks of the elite unit of the National Guard of Panama, just outside Panama City, where the guerrillas and the 62 prisoners of the Somoza regime brought out by them - including Tomas Borge - have been staying incommunicado since arriving in this country on Aug. 25 ("Commander Zero" flew to San Jose, Costa Rica, last Thursday, vanishing from sight).

The two associates of "Zeros" participating in the interview were "Number One," a 31-year-old law student whose name is Hugo Torres, and "Number Two," a 22-year-old medical student called Dora Maria Tellez Arguello, the "political adviser" of the commando unit.

Waiting for "Optimal Conditions"As told by the group, sometimes in lengthy reconstruction of the vents and sometimes in flashes of recollection, the attack on the palace was a carefully planned operation set in motion last May and designed as the culmination of the guerrilla war against the Somoza government that the FSLN had been carrying on in various ways since its secret birth in 1961. The front, which is named after Gen. Augusto Cesar Sandino, who was killed in 1934 after fighting for six years against Nicaragua's occupation by U.S. Marines, had reached the conclusion that the capture of the palace would achieve the twin objectives of forcing the release of its fellow revolutionaries in Somoza prisons and striking a demolishing blow against the regime and its credibility.

What was needed, however, as "Zero" put it, were "optimal conditions" in which the spectacular coup would be executed. These conditions, he said, were provided by U.S. actions at a time when the current phase of anti-Somoza warfare was reaching its high point both in Nicaraguan cities and in mountainous rural areas.

When the front struck in December, 1974, occupying a Mangua millionaire's mansion and taking officials and diplomats as hostages, the political reason at the time was Somoza's reelection to the presidency in rigged balloting.

The year, "Zero" explained, the operation, called "death to Somoza," was delayed until a new set of "objective condition" had developed "Zero" said:

"We decided to strike when we saw the determination of the United States to keep Somoza in power until 1981, the manipulation by foreign capitalists, Jimmy Carter's vacillations, the right-wing support for Somoza in the U.S. Congress, and Somoza's own trip to the United States earlier this year when he returned home being more threatening than ever against the opposition."

"Zero," a powerfully built, squat man, who, at 42, is the oldest in the commando group went on:

"We were terribly surprised by Carter's letter to Somoza considering his decelerations about human rights. How could he praise Somoza while our people were being massacred by the dictatorship? It was clear it meant support for Somoza, and we were determined to show Carter that Nicaraguans are ready to fight Somoza, the cancer of our country. We decided, therefore, to launch the people's struggle."

The rebels were referring to a letter Carter had sent Somoza on Aug. 1, praising him for allowing the human rights commission of the Organization of American States to visit Nicaragua for the first time to study human rights violations.

The presidential letter was sent over State Department objections, foreign service professionals considered -- correctly, as it turned out -- that any gesture toward Somoza would backfire against the United States because of the intensity of the anti-Somoza campaign not only by the front, but by virtually every civic organization in Nicaragua, including businessmen and the Roman Catholic Church. My own impression traveling through Latin America during August was that the Carter letter and an earlier administration decision to release aid funds to Nicaragua despite the Somoza repression has already hurt the American image in liberal circles, to say nothing of the effect in leftist groups in the region.

Recounting the preparations for the attack, "Zero" said that the national directorate of the front -- Tomas Borge is one of its four known members -- had decided that the National Palace would be the target because the hand-picked congress was Somoza's "last vestige of legality" and because it would have "repercussions on a world scale."

It was last May when "Zero" was ordered to return from Costa Rica, where he had lived in exile for years and where he was in charge of logistics for the guerrillas across the border while running a prosperous shrimp business in a small town on the Atlantic coast. He entered Nicaragua clandestinely over the border and presented himself to the national directorate installed in hideouts in Managua. The planning began.

Tight SecurityAt first, only the three members of the directorate in Nicaragua (Borge had been imprisoned for three years, including a three-month period of being hooded all the time) and "Zero" knew the plan -- such was the secrecy surrounding it. In the meantime, the leaders started recruiting members of the commando team. Torres -- "Number One" -- was chosen because he had participated in the 1974 raid on the Managua mansion and because he was ideologically "advanced" and reliable. Dora Maria Tellez -- "Number Two" -- was picked because of her outstanding ideological commitment and her guerrilla experience. Sometime during the summer, "Number One" and "Number Two" were apprised of the plan.

The 22 other members of the team were picked from various guerrilla units in the mountains -- the leadership insisted on regional representation in what was to be the front's supreme effort -- but they learned the nature of the operation only hours before it was launched.

On Aug. 5, the three rebel leaders moved into a house "of regular size" somewhere in Managua. During the next seven days, the remaining members of the commando team were brought to the "safehouse" at the rate of three or four men at a time. Again, security was so tight that the group was divided into two squads -- squad "A" under "Zero" and squad "B" under "Number One" -- and kept totally separated from each other in two section of the house. Only the three leaders (Dora Maria Tellez was attached to squad "B") had access to both groups.

By Aug. 12, the full team had been assembled, and arms -- chiefly German G-3 rifles of 7.62-mm caliber -- and food were surreptitiously brought from the outside. Communications with the front's political leadership were conducted through couriers who came and left once or twice a day. On Aug. 13, a Sunday, the guerrillas watched Somoza assuring the country in a television speech that the army was solidly behind him. "Number One" snickered and said, "We shall see."

Meanwhile, the commandos spent their time in what "Zero" described as "psychological preparation" -- political lectures, simulated combat situations inside a building, assuming firing positions.

The decision to strike on Tuesday, Aug. 22, was made the previous day. The front had learned that the Nicaraguan congress would be in session that day to approve a new loan from the United States and that it would then go into indefinite recess. Since it had already been decided to hit the National Palace as soon as possible after the text of the Carter letter was published, the guerrillas had no alternative but to designate Aug. 22 as the "D-Day."

Still, caution prevailed. On the morning of that day, couriers were sent out to make sure that the congress was indeed going to meet. At 9 a.m., "Zero" told his two deputies, "This is it." The leaders assembled their teams, had them don the Nicaraguan army uniforms that were used in the operation, and the guns were loaded. At 10:30 a.m., "Zero" briefed his squad and "Number One" briefed his unit an hour later. "Zero" recalled: "There were all drunk with happiness about the mission."

Two oliver-green pickup trucks drew up at the door of the safehouse. Lookouts provided by the front covered the squads as they jumped into the trucks and pulled down the tarps. Looking back at the operation, "Zero" said that the only time of danger he had anticipated was during the trip from the safehouse to the palace.

But the guerrillas aroused no suspicions and, at 12:25 p.m., precisely the time set in the plan, one truck pulled up at the side door on the east of the palace and the other at the side door on the west side. The men jumped out of the trucks and hurried toward the entrance. Wearing uniforms of the army's training battalion, they went unchallenged past the guards at the doors, although at the last moment a soldier suddenly became suspicious and turned his rifle on the squad led by "Zero." He was shot dead at once.

Once inside the palace, the two squads rushed upstairs to the Hall of Congress. When soldiers posted downstairs at the main entrance to the building fired at them, the guerrillas responded with machine gun bursts, killing five.

"Zero" led his squad into the congressional hall, firing rifle bursts over the heads of the congressmen, shouting "Hit the ground!" The congressmen threw themselves under their desks. "Zero" recalled" "When I reached the president's desk, he said, 'What is this?', and I replied that this was the people's army." At that point, the guerrillas covered their faces with red-and-black kerchiefs, the colors of the Sandino front.

A War Until Death"You know what happened afterwards," the commander said. The rebels issued their demands for the release of prisoners in Somoza jails, the broadcast of radio and television of their revolutionary program, and $10 million.

As the negotiations began, "Zero" gave the regime six hours to meet his demands, a period subsequently increased to 13 hours, the most critical period of the occupation.

"If the emissary, the Archbishop of Managua, hadn't come back with an acceptance at the end of the 13 hours, I was ready to start the executions," the commander told me. "And we would start massive executions at once if the Somoza army had attacked us."

"Zero" said that although he thought that the throng in the building constituted a form of protection for the rebels, "I couldn't be sure of Somoza's reactions. So we were ready." In fact, he had drawn up a list of execution victims. It was headed by Luis Manuel Martinez, a Cuban refugee close to the Somoza regime, the acting chairman of the congress, Luis Pallais Debayle, who is Somoza's first cousin, Jose Somoza Abrego, who is Somoza's nephew, interior minister Jose Antonio Mora, and deputy interior minister Adolfo de la Rocha Hidalgo. They were to be followed by 60 members of Somoza's liberal party who were in the hall. "Zero" said that there was never any intention to harm others in the building.

There was a certain sense of unreality as we sat in the Panama National Guard barracks a week later, calmly discussing the operation and the planned execution. At one point I asked "Zero": "Were you really, but really, going to kill 65 men in cold blood?"

He stared at me with a hard glance. "Yes," he said. "No question about it. It would have been an act of justice. It would have avenged our murdered brothers and sisters. But, of course, the principal thing was to liberate our companeros, and I hoped that this would happen and that we would not be pushed into the executions. You must understand: We are fighting a war until death."

"Zero" said that the $10 million demand was the least important of his conditions, and that this was why he had agreed to only $500,000 in cash delivered to him at the palace.

The guerrillas would not be drawn into discussing how and where they had obtained funds to mount the operation and acquire arms. But the front has had an ample supply of arms for a long time, and the strike at the congress was not a mission requiring large sums.

"We did it our way," the commander said, "Now let us think about the future."

Szule is a Washington-based writer on foreign affairs. His latest book, a history of U.S. diplomacy in the Kissinger years, is "The Illusion of Peace."