Six weeks after their daring assault on the National palace in Managua that set off a civil war, Nicaragua's Sandinista guerrillas say they are anything but defeated.

Despite the massive National Guard air and artillery retaliation that put down civil rebellions they led in cities throughout Nicaragua, Sandinistas and their leaders interviewed in a remote hideout last week claimed to have emerged with their numbers swelled and their support among the citizenry near universal.

The Sandinistas said that in this guerrilla camp and others inside Nicaragua and in nearby countries, they are training for another attack on the National Guard and its leader, president Anastasio Somoza. Although they will not say when or where the attack will come, they believe its domestic and international repercussions will equal those of the palace raid and bring them closer to toppling Somoza.

The camp is hidden far from the nearest city, a long highway drive and another hour by jeep across fields and forests to a collection of old, weathered buildings.

Concealed armed guards announce the approach of a stranger long before the buildings themselves can be seen, in plenty of time for their occupants to muster to battle stations.

It is late morning and 50 or 60 Sandinista troops are drilling in an open field, sweating in mismatched green fatiques and blue jeans, trampling over rows of newly sprouted vegetables. They carry an assortment of U.S.-made World War II vintage rifles and the new, dull-grey Israeli and Europeans automatic weapons bought on the black market or "liberated" from the National Guard.

Up on the wide, shady porch of one of the barracks-style buildings, others explain that the drills are for a special purpose. One of the guerrillas, a photographer, is taking pictures of the troops for publication in the Sandinista newsletter, to be distributed by sympathizers abroad.

The newsletter, and the decision to allow a reporter to visit this camp, are paert of a new Sandinista policy to "show our faces to the world," one guerrilla leader said. The only condition placed on the visit was that the location of the camp not be revealed.

Somoza has called the Sandinistas Havana-controlled and Moscow-backed communists, and U.S. congressional conservatives have labeled them "Marxist revoluntionaries" who seek to turn Nicaragua into "another Cuba." The Sandinistas, however, say they are "mature, conscientious Nicaraguans" who are fighting for and willing to work within a "pluralistic democracy."

Ideology aside, there is little doubt that the Sandinistas, as a fighting force and the symbol of widespread anti-Somoza feeling, have become perhaps the most decisive factor in Nicargua's future.

When the long-smoldering flames of opposition were ranned by the assassination last January of anti-Somoza newspaper editor Pedro Joaquni Chamorro, the Sandinistas launched a series of attacks against the National Guard that culminated in the August raid on the most important government building, and brought public emotion to the point of nationwide rebellion against Somoza last month.

The Sandinistas now say they had little to do with organizing the "spontaneous rebellion" of Nicaraguans in cities throughout the country. If they had planned it, one guerrilla leader said "the people would have been better armed and better prepared." It was only after the extent of the National Guard retaliation was seen, they said, that their commandos stepped in to organize and lead the population.

While the number of civilian casualties has been estimated in the hundreds, and perhaps thousands, the Sandinistas claim their own losses in the battles were slight - fewer than 20 combatants killed. Their net gain in new members in the past several months, they claimed, swelled their ranks to more than triple their earlier estimated strength of 200.

The guerrillas here at the camp are a broad collection of diehard revolutionaries and longtime mountain fighters well educated young capitalists and leftist ideologues, peasants, students and workers.

Among the more than 150 living here are Alejandro, a 30-year-old industralist whose father is an opposition member of the Nicaraguan Senate; Nora, a 29-year-old attorney and mother of two; Ramon, 25, a shoemaker from Matagalpa; a Nicaraguan-born poet who grew up in California; at least one priest and Eden Pastora, the 42-year-old "Commander Zero" of the palace assault and the most wanted man in Nicaragua.

The camp is frequently visited by a series of transient supporters, including the recently resigned Panamanian vice minister of health, the son of a Honduran political leader and an assortment of local citizens who have offered the Sandinistas homes, vehicles and logistical support.

Although Somoza has said the Sandinistas receive foreign communist backing, the guerrillas said the money to finance their camps and operations comes from supporters primarily in Latin America and Nicaragua itself. Last week, for example, a benefit concert, with all proceeds going to the Sandinstas, filled a stadium in Mexico City. In Costa Rica, student groups have set up Sandinista street stands selling snacks, souvenirs and literature.

Nora is one of six or seven women in the camp, and is three months pregnant. Sitting under a shade tree away from the main buildings, she explained why she is here.

"We are first Sandinistas," she said. "That means, among other things, that we are fighting for a new Nicaragua. It doesn't mean a new Cuba.

"I studied law in Managua, and became an attorney for a large construction company. There is nothing special about me - I spent two years studying in the United States and in Europe. I was part of the privileged class.

"It was easy to see, in my own profession, the way the Nicaraguan government operates. The injustice, the corruption. My own job was to find ways for the company to avoid paying taxes. For years, I tried to change things legally, in a civic struggle, and I saw that it was all impossible.

"I realized that, no matter how good, or how dedicated one person can't fight alone. And I saw the Sandinistas as the only organization that had a hope of success."

Early this year, Nora was approached by Sandinista friends with a plot to assassinate the second-ranking general in the National Guard. She began making business trips to his office, where his many jobs included supervision of certain government contracts involving her company.

In time, she said, she convinced the willing official of her sexual interest in him. One night, she invited him to her home, and as she met him in an embrace, her waiting comrades shot him through the head.

"The initial decision to fight is the hard one," she said. "After that, it comes easily. But nobody likes this war. We know that the people we are killing are also Nicaraguans, and that are own friends are being killed."

Last month, Nora was among the Sandinista troops who invaded Nicaragua across the Costa Rican border.

Despite the camp's guards, there is little sense of expected threat. Most days, the Sandinistas go about their business in an almost boring routine way. Up at 4:45 a.m., they exercise, train and study, with short breaks for meals and cleaning weapons. By 9 p.m., most are asleep.

No liquor is allowed and cigarettes are often at a premium. Food is a spartan serving of rice and vegetables - occasionally augmented by "liberated" beef from an unlucky cow - served on anything from tin plates to trashcan lids and eaten cross-legged in the fields.

The walls of the barracks are bare, except for hand-written copies of camp rules, and reading matter appears to be confined to novels and copies of the 25-point Sandinista political program.

A bulletin board has newspaper clippings of Somoza speeches and stories about Sandinistas captured in Honduras, where the military government jails them, and in Costa Rica, from which they are usually deported to Panama and quickly make their way back to their home camps.

The isolated silence of the camp is broken only by shouted commands from the drill field and the heavy clunk of weapons set down on wooden floors. Ammunition is not wasted on drills.

Although there is a near-constant shuttle of supplies in and out of the camp - food and cardboard boxes filled with ammunition and radio equipment - many of the guerrillas have not seen their families for months. Most have not made the jeep trip even to to the highway since the final battles of last month's fighting.

Training is conducted by the old hands at guerrillas fighting, like Pastora, who teaches strategy, firing positions and weapons handling. Except for occasional minor strikes at National Guard outposts, the Sandinistas said, they are spending their time "resting, regrouping and training" the new members, many of whom said they had never shot a gun before last month's battles.

Roberto, a 32-year-old chemical engineer who has left his wife and children in Mexico while he fights with the Sandinistas, said he began giving support to the guerrillas six years ago, when he was trying to set up a business in his Nicaraguan home town.

"There was the repressive National Guard," he said, "and of course the corruption. The fact that children go hungry in a country with hugh national resources, and people die from incurable diseases. But those weren't really my reasons" for joining the guerrillas.

"Most of all, it was a lack of a functioning infrastructure" in Nicaragu. Roberta said he lost almost $60,000 when he tried to set up a business that never got off the ground because the government light and power company could not manage to hook up electric current to his factory in the space of a year.

"You go to other countries," he said, "and you see the advances they have made. And you come back here, and it makes you feel sorry for Nicaragua. I started reflecting on it, started getting more emotional about it, and I realized that Somoza simply cannot continue here. And it's not only Somoza; it's the whole structure."

Despite the large number of professionals and university-educated Nicaraguans here, the bulk of the Sandinistas are from lower economic classes.

Ramon, the shoemaker, sat on the porch with his M1 rifle propped against his knees. His wife and two children, he said, live in Costa Rica, where he said he can make three times as much money as in Nicaragua.

Ramon said he has been with the Sandinistas for two years now and, when he's not fighting or drilling, spends most of his time "sitting and studying the history, and the program."

His main goal in life, Ramon said, is to go back to Nicaragua and make shoes. "I'll go back," he said."We'll all go back."