On the tape the voice is measured and slow, speaking what sounds like a Spanish carefully pronounced for the foreigner outside the prison. It is the second time in a year that this man has spoken to the press, and he must now do it indirectly, from his cell, with a conduit carrying the written questions in and the finished cassette out. His cassette had contained recorded Latin music, some smooth cocktail-loungey melody, and he seems to have waited for the piece to end before starting to talk, so that the final unlikely effect is of a polished musical introduction to a voice identifying itself as Comandante Uno, the man who held two dozen diplomats hostage here for two full months of 1980.

"I was born in Cali, the 11th of July, 1948," says the voice. "Our family was nine brothers, including me. I only knew four. Another four died when I was small . . . The situation was a little precarious, and I remember that my mother took in ironing and laundry to help my father sustain us . . ."

In the background there is occasional yelling, with the resonance of shouts echoing in a place without much furniture. A second voice reads the questions, ignoring some and inserting others that were never written. The second voice is softer than the first, and begins each question with what appears to be the correct honorific: "Comandante."

Sunday is visiting day for women who wish to enter the Bogota Federal Penitentiary, a low and oddly pastoral-looking collection of white buildings and barbed wire surrounded by the mountains and cow pastures that always seem to glisten deep green during the Colombian rainy season. Up the muddy entrance path, their arms laden down with heavy shopping bags full of cigarettes and bananas and still-warm soup pots, small women step quickly in flat-soled shoes which many of them keep precisely for this occasion. High heels, which might contain contraband, are forbidden -- as are reporters, in this season of Colombian edginess, and foreigners, and anyone readily identifiable as a colleague of the celebrated guerrillas the Colombian army has finally hauled inside the penitentiary walls.

They have captured Carlos Toledo Plata, the white-haired orthopedist and former member of parliament who had disappeared three years ago into the underground hierarchy of the movement called M-19, his name at the top of those claiming responsibility for a massive and remarkably well executed theft of 4,883 Colombian army weapons. They have captured Rosenberg Pabon Pabon, the schoolteacher from southern Colombia who adopted the name "Comandante Uno" and led last year's 61-day siege of the Dominican Republic embassy.

The Colombian army has crippled, if not broken, South America's most famous active guerrilla movement. Long after the defeat of the Argentine Montoneros and the Uruguayan Tupamaros, the M-19 was still pouncing on the Colombian public with its vague but passionate cries for nationalism and social justice. The captures and trials are being followed with rapt attention by almost every Colombian who listens to a radio or reads a newspaper. Despair at the political system is endemic in this lumbering democracy, and for a startling array of otherwise conventional Colombians, the M-19 has always been the one group capable of an occasional satisfying swipe at the national power structure.

A political writer for one of Bogota's firmly pro-government dailies said that, when he heard that the two guerrilla leaders had been captured, "My first response was: 'What a shame.'" He said, "You heard that from all sorts of people -- 'What a shame.'"

It has been a little over a year since the M-19 first crashed its way into international headlines by storming a diplomatic reception and taking 32 hostages. Most of the hostages, including then-U.S. ambassodor Diego Asencio, were diplomats. Two young men were killed in the initial shooting, one a teenaged M-19 member and the second a student apparently caught in the crossfire. For the next two month, as the hostages ate, slept and wrote letters inside the ill-equipped old building, the Colombian government worked furiously to stave off further bloodshed without acceding to the demands of a guerrilla organization that up until February 1980 had hardly ever been heard of outside Colombia.

What they wanted was the release of 311 colleagues they described as political prisoners, plus $50 million, plus full amnesty for all concerned. They got neither the prisoners' release nor the money (though $1 million to $2 million is said to have been raised in private ransom), but were finally granted safe passage to Havana, where they hugged their ex-captives in an extraordinary airport goodbye scene and then, apparently, disappeared into the welcoming arms of the Cubans.

Then, this spring, in a drama that splashed huge headlines and photographs across every major newspaper in Colombia, Pabon Pabon and Toledo Plata were taken prisoner when their defeated guerrilla columns, surrounded by thousands of army troops, backed across the border into Ecuador. A boat called the Friedi had carried the guerrillas down through the Pacific from Panama, and upon landing they had unloaded into the inhospitable swampland of the Colombian coast, armed with a newly acquired weapons collection that reportedly included mortars and German-made automatic rifles.

Until this year, the M-19 had seemed a throwback to the early 1970s, when urban guerrillas like the Tupamaros and the Montoneros had helped bring international attention and violent military repression to the southern cone. Now the M-19 was trading fire with army soldiers in the damp Colombian bush -- acting, at least in the eyes of the military, like the Salvadoran or Guatemalan guerrillas.

It was a tactical disaster for the M-19. New at rural fighting, thinned by deaths and injuries, and trapped in a giant circle of Colombian army troops, the M-19 columns fled Colombia, hoping the Ecuadorians would grant them what Pabon Pabon called "temporary political asylum." In the town of San Lorenzo, Ecuador, according to reports of the incident, one M-19 column surrendered to what it thought were Ecuadorian troops, only to find that they were in fact similarly uniformed Colombians. A second group did surrender to the Ecuadorians, but the Ecuadorian army, in what some Colombians have said was a violation of international agreements, immediately handed its prisoners over to the gratified Colombian troops.

Now, at last, the army had two of M-19s three "maximum leaders." The only one still at large was Jaime Bateman Cayon, a 34-year-old man from the north coast town of Santa Marta. Jaime Bateman, according to the most recent M-19 missives from underground, has declared himself a candidate for the presidency.

The battles and captures and trials of the April 19 movement, as the M-19 calls itself in its more formal moments, have become something of an obsession both in Colombia's newspapers and its political machinations. The country endured a 20-year undeclared civil war of extraordinary barbarity after the populist presidential candidate Jorge Gaitan was assassinated in 1948, and it had grown comparatively numb to political violence by the mid-1970s.

The M-19, after all, is only one of nearly a half-dozen guerrilla groups that have worked for years, sometimes at cross-purposes, in the enswelling cities and lush mountain countryside of Colombia. The best known of the others, the Colombian Revolutionary Armed Forces, was once said to be loosely linked to the Colombian Communist Party and as of last month, according to a brief newspaper item, was holding five kidnaped people in various towns outside Bogota.

But it is the M-19, with its ranks of university graduates and its flair for the dramatic, that dominates the headlines now. Whether they are beaten, or broken, remains as much of a mystery as the apparent turmoil within their ranks. When American linguist Chester Bitterman was kidnaped last January and murdered after six weeks in captivity, his killers identified themselves as the "M-19 National Base Command." The M-19 "maximum leaders," who had at that time not yet been captured, immediately released a communique which denounced the killers as "militants with a bellicose and terrorist spirit," said they had stolen the name M-19, and conveyed the movement's sympathy to the Bitterman family.

Some weeks later, the new U.S. ambassador, Thomas D. Boyatt, received a letter signed "M-19" threatening him and his family with death if he did not leave the country. The letter closed with demands for the liberty of Toledo Plata and Pabon Pabon. As of last week, the imprisoned M-19 leaders appeared to have nothing to say about it.

But in random conversations with Colombians, a stranger hears little about death threats and the M-19's acknowledged murder of union leader Jose Raquel Mercado in 1975. Instead, people talk about the M-19 as a band of Robin-Hood-like adventurers. They used to commandeer mild trucks and deliver free milk to poor neighborhoods, people say; they used to hold business executives captive in "people's prisons' until their employes were granted pay raises.

"I think the M-19 is a symbol of desperation," said former foreign minister Alfredo Vasquez Carrizosa. The desperation reaches both the spirit and the gut. The country still holds millions of people who cannot read, find jobs or adequately feed their children. Adult illiteracy is estimated at 35 percent of the population; the levels of infant mortality and children's diseases are very high. And the two-party civilian democracy, which lumbers along under the constraints of a stifling nationwide patronage system, has been dubbed by a Colombian journalist "the politics of anesthesia."

Into this atmosphere of generalized frustration came the April 19 movement, preannouncing its arrival seven years ago with a series of newspaper advertisements that said mysteriously, "Wait for M-19."

"Nobody knew if it was something to clean your floors with, or cigarettes, or what," Vasquez said. On Jan. 19, 1974, they found out: M-19 members stole the sword off the statue of the South American liberator Simon Bolivar, declaring that the Colombian government "did not deserve to keep it".

They had taken their name from the election of April 19, 1970, when the former dictator Gustavo Rojas Pinilla narrowly lost his campaign to regain the presidency. Under the aegis of the National Popular Alliance, Rojas Pinilla had run on a platform of intense nationalism, promising a vast increase in jobs and social services. It was a rhetoric not unlike that of Gen. Juan Domingo Peron, then the aging phoenix of Argentine politics, and it rang particularly true to Toledo Plata, who had become deeply enamored of Peronism while attending medical school in Buenos Aires.

"The National Popular Alliance won the election," Toledo Plata said from his prison cell. "Nevertheless, the oligarchy, the liberals and conservatives, organized a fraud and stopped the people from choosing . . . I think that was the moment when I decided I had to look for a political movement with military organization, to create a clandestine group and start fighting using these methods."

At the time, Toledo Plata was a 37-year-old member of Parliament.Today he is one of approximately 75 co-defendants (the numbers grow as new guerrillas are captured) undergoing military court-martial, charged with the crime of rebellion. Toledo Plata has also been charged with arms robbery -- he has publicly taken credit for helping mastermind the massive weapons theft in 1979 -- and three political kidnappings.

Inside the plain-looking penitentiary chapel, the only room big enough to hold the defendants and their families, a military prosecutor is slowly laying out his version of the history of the M-19: How the guerrillas rented a private home near the weapons cache, pulled out the kitchen floor and carried the dirt out in cartons as they began digging their famous tunnel; how aspiring M-19 members must take an eight-day to two-week "ideology" course; how the organization maintains a precise and military internal structure.

The press has been barred from the proceedings, so it is difficult to know precisely what is going on inside now. Toledo Plata's lawyer, a Conservative Party member and former Supreme Court justice who says he shares his client's contempt for the current Colombian government, says his defense will be "to accuse the society that judges him."