On the morning of Oct. 15, 1979, a group of young Army officers in El Salvador informed their president and commander-in-chief, general Carlos Romero, that he had until 3 p.m. to turn over the government and leave the country. The ultimatum spelled Romero's doom and an embryonic foreign policy crisis for the United States.

Romero consulted the U.S. Embassy, his headquarters and regional commanders. Finding he had no support, the general and his aides packed their bags and were gone without a shot being fired.

Three days later, a new government composed of two relatively unknown Army colonels and three civilians presented itself to the Salvadoran people and proposed a bargain. After nearly five decades of right-wing military dictatorship and domination by the rich, they pledged radical changes in the country's "social and economic structures," political pluralism and an "immediate end" to military corruption and repression to the left and peasantry.

In return, this new junta asked only "patience, understanding" and the confidence of the Salvadoran people.

Thousands of miles to the north, middle-level State Department officials, who had feared an imminent takeover of the Central American republic by leftists guerrillas, breathed easier. The Carter administration issued a statement pronouncing itself "encouraged."

Today, 16 months after that relatively obscure event, the tropical backwater that Spanish Catholics named after "The Savior" is the front line in the world's principal power struggle. Two successive U.S. presidents have made it a leading foreign policy symbol, and many Americans, their concern over little-understood wars in little-known lands reawakened, are beginning to fear their sons may be asked to die on its volcanic slopes to preserve freedom in the Western world.

With a suddenness that has stunned many in this country, Ronald Reagan and Alexander M. Haig Jr. have defined El Salvador's insurgency as a conflict with global meaning, asserting that Cuban adventurism and "international terrorism" have created a crisis in America's "front yard" that must be confronted. U.S. allies have been put on notice that El Salvador is the first important test of their willingness to cooperate with Reagan.

White House officials, while denying that the new administration was looking for an early crisis to show its toughness, agree that El Salvador's problems provided a "fortuitous coincidence" for just such a demonstration. El Salvador, these officials say, is "the first step" in a conscious effort to "repair" America's image abroad and to project a determination to control world events in a way that the Carter administration did not. The Soviets, the Cubans and the Palestine Liberation Organization are all targets of American actions in El Salvador now.

For Jimmy Carter, El Salvador was a different kind of testing ground, one that exposed the multiple, often conflicting sides of a policy that will likely be remembered as both the best and worst of his administration. El Salvador was a place where Carter could prove that abusive governments did not deserve United States friendship or support, and that improvements in the way they treated their people brought U.S. praise and aid.

With the repressive Romero regime gone, El Salvador became a country where the United States would demonstrate it could tolerate, even encourage, the kinds of reforms proposed by the left. If El Salvador's government could be pushed into preempting the best of what the left had to offer in terms of economic and social equity, the theory went, those who wanted to seize power for the left would have little to offer except communist authoritarianism, violence and international isolation.

Carter's stress on reform and Reagan's on combatting international terrorism are different reflections of a new domino theory. Central American-style. Each version represents a response to U.S. political realities as much as they reflect what is going on in El Salvador. This two-part report will examine both sets of realities in the light of the importance the new U.S. administration has attached to a crisis it says it inherited from its prececessor.

Perhaps because of the very obscurity of El Salvador -- the fact that its problems had been left to fester for a half century -- it provides a near-textbook case for testing both the reformist tendencies of the Carterites and the counterinsurgency techniques Haig seems to favor. The stakes are not oil or mineral wealth, of which El Salvador has none, nor are they U.S. private or government financial investment, of which it has little. At issue are geography and politics. El Salvador is close, in the U.S. front yard, and, traditionally, in its sphere of influence. The Junta

El Salvador is a land of superlatives, most of them negative. Wedged into the Pacific coast, it is the smallest and most densly populated country on the American mainland. It is also one of the poorest nations in the hemisphere, and its political history is one of the bloodiest. As conservative, upper-class Salvadorans never tire of reminding newcomers to their battles, El Salvador was the site of "the first Bolshevik revolution in the Americas."

By most accountings, more than 30,000 lives were lost when the Army cracked down on that 1932 uprising. Peanuts, led by local Communists, launched a disastrous revolt against landowners -- then a group of 14 rich and ruling families who ran the country as a virtual feudal state. The event, and its outcome, wrote the script for the current Salvadoran drama that last year took the lives of more than 10,000 Salvadorans -- among them thousands of peanuts as well as guerrillas, soldiers and some of the best and brightest the country had to offer.Today, the principal actors are largely the same: an entrenched landowning class with a stridently anticommunist armed forces to defend it, and a repressed peasantry with its largely self-appointed communist-based defense squad.

It was only in the late 1960s and early 1070s that a new group of players began to take increasingly important roles. The Roman Catholic Church, long a powerful ally of the landowners, suddenly became a spokesman for the poor. A class of civilian politicians, most of them moderates or left of center, emerged to challenge the political power of the military. More recently, foreign powers began to take more than passing interest.

The biggest surprise, in the Salvadoran context, was that a group of young military officers began to see that their country was a socio-economic version of the bubbling volcanoes that dot its landscape.

The ultimatum that drove Romero from the shady, breeze-filled presidential palace that perches on one of the only hills in the sun-scorched capital of San Salvador brought to power a five-man junta that held precisely such views. Their outlook had been formed in a decade of turmoil, in which unprecedented presidential victories by civilian candidates in the 1972 and 1977 elections had been overturned by a military establishment that had been accustomed simply to rigging the elections for its own candidates. But president Arturo Molina, an Army colonel, and his successor, Romero, had been increasingly obliged to use force as a means of putting down public protest.

Groups of leftist guerrillas had formed and had launched a wave of bombings, kidnapings and direct attacks against military installations. Increasingly, their efforts were backed on a political level by a broad spectrum of striking industrial and peasant unions, professionals and intellectuals. Right-wing paramilitary squads backed by the military, and the military itself, answered the left in kind with a wave of repression against peasants, the church and politicians.

In the United States, which had long backed the military with weapons, training and recognition of its political legitimacy, first the Congress and then Carter were up in arms over something they called human-rights abuses. An Organization of American States human rights team, which had visited El Salvador in 1978, reported in January 1979 that government security and paramilitary organizations were responsible for the deaths of "numerous persons," as well as for acts of physical and psychological torture and inhuman imprisonment in secret dungeons.

But these were relatively minor annoyances compared to the shock wave that hit Central America's military governments in July 1979, when Nicaraguan president Anastasio Somoza, the regional right-wing patriarch who was considered a favored U.S. son, was otherthrown by a popular insurrection led by guerrillas of the Sandinista National Liberation Front.

Not only did the left win a military victory in Nicaragua, it proceeded to throw thousands of members of the Nicaraguan National Guard, once thought an invincible force, into prison. And the U.S. president said it was all right by him.

"What happened in Nicaragua was the force behind the coup in El Salvador," said one former Salvadoran government official with close connections to the young officers' group. "The officers saw what happened to the National Guard. They didn't want to risk a confrontation with the left. tAnd they were scared of Carter."

In a different sense, it was Nicaragua that also brought the United States right into the Salvadoran political thicket in a way that continues to entangle Reagan. Somoza's fate clearly suggested to Washington policy makers that Romero was on the endangered species list as well.

Although the State Department hotly denied U.S. involvement in Romero's overthrow, observers in Washington and San Salvador noted that little happened within the American-trained Salvadoran military without the United States knowing, and approving, in advance. While it was willing to live with a leftist government in Nicaragua, according to State Department officials at the time, the Carter administration was not prepared to countenance a similar takeover in El Salvador, and was convinced the only way to avoid it was to get rid of Romero and what he and the military establishment represented there.

In one three-week period before the Salvadoran coup, William Bowdler, a U.S. diplomat who had served as Carter's chief troubleshooter in Nicaragua, visited Romero twice. Viron P. Vaky, then the State Department's top expert on Latin America, made at least one unpublicized trip to San Salvador. Both took a hard line with the general, strongly advising an immediate political opening to the nonviolent left and center, substantial advancement of presidential elections scheduled for 1982, and changes in the country's economic and social structures and strong action against human-rights abuses perpetrated by government forces.

But there were some things Romero -- the tenuous head of a fearful and bickering hierarchy of high-level officers, low-level assassins and large vested interests in the private economic sector -- could not change, and others that he would not.

Sitting in the heavily fortified U.S. Embassy several days after the coup, then-ambassador Frank Devine allowed that "we, like everybody else, were aware that some changes were coming."

The young, reform-minded officers, primarily captains and majors in the Army, plotted well. They consulted not only the United States, but the powerful Jesuit community of leftist intellectual priests, and the office of San Salvador archbishop Oscar Romero, a leading human-rights advocate unrelated to the deposed general of the same name. Reluctant to take power themselves, they named two ostensibly like-minded colonels, Jaime Abdul Gutierrez and Adolfo Arnoldo Majano, to lead the junta.

To prove their pluralistic intentions, they appealed to some very specific civilians to join. Guillermo Ungo, head of the small social democratic National Revolutionary Movement and the 1972 vice presidential candidate, was brought in to represent the "Popular Forum." An alliance of 14 political and union organizations, the forum included both the dominant opposition Christian Democratic Party and the National Democratic Union, the recognized legal front of the Salvadoran Communist Party.

To represent the church and the intellectuals, Roman Mayorga, rector of the Jesuit-run local branch of the University of Central America and an eloquent human rights spokesman, was added. The junta was rounded out with Mario Andino, a local businessman who represented the least conservative faction of the private sector.

In the abstract, it seemed a dream team. But within a week, the issue that had brought Carter's attention to El Salvador in the first place -- human rights -- would show that the new junta was too divided, and too weak, to make the changes that would win it credibility and a chance to survive.

Among the touchiest issues of the day in El Salvador were charges by the Catholic Church and human-rights groups that hundreds of persons had been secretly arrested for political reasons by the Romero government and its predecessor. Many, it was charged, were being held in secret jails; most had been tourtured and some were dead.

Romero had consistently denied having any political prisoners at all. But it was indicative both of the dubious quality of his denials and the good will of the new government that the first decree issued by Majano and Gutierrez ordered the release of "all" political prisoners -- a number they did not specify -- and the punishment of those armed forces members who illegally arrested, tortured or killed them.

Eight days later, the junta announced that it could produce no prisoners, and junta members, with great embarrassment, told families lookig at least for confirmation of the deaths of those known to have once been in the hands of the security forces that they could not help. Later, Gutierrez told reporters that he was concerned about the supposed prisoners, but that the government also had "other priorities," in particular the continuing attacks from the leftist guerrillas that, even as he spoke, were going on in a slum outside the capital. g

Ungo told reporters he was "worried." The military

There are many Salvadorans, particularly those who initially had faith in the new government, and later lost it and joined the left, who say that the battle for peaceful democratic change in their country, and avoidance of civil war, was lost in those first two weeks.

The young captains and majors had thrown out of the country not only Romero, but all of the Army's generals and most of its colonels. But, according to many informed observers at the time, the captains, imbued with a sense of command structure and a rigid view of their own institution, were "afraid" to take over themselves.

In addition to Majano and Gutierrez, they left a number of other colonels, some of them garrison commanders outside the capital, in positions of command. At the time, the most objectionable of the colonels, in the view of government civilians, was newly appointed Defense Minister Jose Guillermo Garcia, a one-time presidential hopeful during Romero's reign.

Perhaps more importantly, in hindsight, they left the Salvadoran security forces virtually untouched.

To understand the military mindset and repression in El Salvador, and to make at least partial sense of current, bewildering charges and countercharges of death squads, paramilitary forces and "who is killing whom," one must go back to the maze-like system of military bodies that is peculiar to that country. In this maze also lies either a success or a disaster for Reagan's determination to show that U.S. military aid is a key to defeating guerrilla infiltration and subversion in Central America.

The Army, a force of about 7,000 men, is technically charged only with defending the country's borders from external aggression. At the same time, there are also a number of separate police bodies known collectively as the "security forces."

Chief among them is the National Guard, an institution whose structures and functions are modeled on those of the Spanish Civil Guard. Where most of the soldiers in the Army are draftees and their current commanders are young products of the Salvadoran military academy, the rank and file in the National Guard are older career men. Most of them have served since the days of the dictatorship when they were given a free hand to keep order and mount domestic military operations in the name of fighting communism.

Their garrisons are dotted throughout the country, in areas where, to greater and lesser degrees, their commanders operate virtual fiefdoms of control.

The National Police is a smaller organization, primarily providing police functions within urban areas, but in some parts of the country controlling smaller villages. In addition, the Treasury Police have broad investigative authority and wide opportunities for graft.

Under the old, now ostensibly disbanded system of military rule, according to Salvadoran sources close to the military, each of these bodies also had a wide system of informers and paid thugs among the civilian population, as well as death squads, under the direct order of the executive's office of intelligence, to eliminate troublemakers and suspected subversives.

Far-flung security units, often out of touch with any central command structure, tended in many cases to operate virtually as the personal police forces of local landowners, the ultimate economic power behind the military throne. They were, and in some cases continue to be, more accountable to the landowners than to their superiors in San Salvador.

The frail command structure and conflicting loyalties in the4 Salvadoran armed forces are a problem frequently cited by U.S. military officials working with them. An example last summer illustrates the contention of some U.S. officials that a large U.S. military program might only make the problems worse. Eight workers of an agricultural cooperative, organized for peasants under the new government's land-reform program in a place called El Penon, were shot to death.

According to area residents, National Guard troops -- apparently out of loyalty to the former landowner whose plantation the reformist government had seized, dislike of the reforms themselves or a belief that agricultural reformists were leftists -- entered the cooperative in the early morning and murdered its entire leadership. Later, the local Army unit, which was friendly to the cooperative leaders and some of the agrarian reform officials, came to the farm to protect its inhabitants -- most of whom had fled in fear.

Subsequently, other killings occurred, and both the local National Guard and the Army began to demand protection money from the peasants of the cooperative. The killing has slacked off.

Although the U.S. government under both Carter and Reagan has argued that its military aid is necessary to better train the Salvadoran armed forces, there has been "very little" progress in teaching it not to kill noncombatant civilians, according to another recent U.S. ambassador in El Salvador, Robert E. White.

In testimony two weeks ago before a congressional subcommittee in Washington, White argued against sending more U.S. armaments there and said that "the greatest disadvantage" El Salvador's struggling government now has "weighing it down are the excesses of the security forces."

According to informed Salvadoran sources, the death squads of each of the security forces remains intact, under the direct control of the Army. The remaining vestiges of the old system of diffused authority and separate powers, these sources say, also allow the highest government levels to retain what a U.S. official calls "deniability" of the worst military abuses. rAsked if he thought Defense Minister Garcia ordered, or knew of, their activities, the official said , "I just don't know."

Whatever military values the United States wishes to instill in the Salvadoran armed forces will have to overcome decades of their own training. Boot camp manuals used at least until the time of Romero's departure describe, in primitive drawings and language, the subversive tendencies of young people with uncombed hair, and priests who wear local peasant clothing rather than the traditional collar or cassock.

For years, as the United States trained the Salvadoran officer corps, they were taught that their primary function was to prevent the spread of communism. Suddenly, the Carter administration, as one high-level Salvadoran intelligence officer said just before the coup, "doesn't think we know how to make reforms at the same time.

"We will have democracy," he said, "but a lot of people will have to die here first."

The process of reforming the armed forces under the new government has been additionally complicated by the emergence of a wide variety of so-called right-wing extremist elements -- freelance death squads ostensibly up for hire to the highest bidder. The extreme right first became visible in 1977, when a clandestine group calling itself the "White Warriors' Union," belived at the time to be an offshoot of the right-wing "White Hand" movement begun in Guatemala in the 1960s, threatened to execute all Jesuit priests if they did not leave El Salvador by a stated deadline.

The deadline passed, and nothing happened. But in the intervening years, other groups emerged under other names, with real victims. In numbers that increase daily, the dead are found alongside rural roads and on city streets corners, often with a group's initials carved on their multilated bodies or placards strung around their necks.

According to White and other analysts -- although no proof of their beliefs has been made public -- the extreme right is financed from Miami and Guatemala City by wealthy Salvadorans who fled the country under the new government, who dislike its socialist reforms and who hope to regain what they have lost by inciting chaos, economic ruin and an eventual right-wing military coup. Their ostensible leader is former major Roberto D'Aubuisson, second in command of Army intelligence before he became one of the few such officers to be ousted along with Romero. D'Aubuisson, in public statements inside and outside El Salvador, denies any connection with the extremist death squads and says merely that he wants the civilians out of the government.

White describes D'Aubuisson as a "psychopathic killer." White, along with opponents of the junta, believes that the fact the former major is known to have plotted at least two attempted overthrows of the current military-civilian coalition government, that he was arrested on good evidence of such activity last year and quickly released by the military, and that he still walks the streets of San Salvador, provide strong evidence for what many charge is a very thin line between the right-wing extremists and active-duty members of the armed forces, if any line at all. The Left

At the time of the coup even the Salvadoran military was willing to admit that the threat posed by the violent left was composed of a few hundred hard-core cadres with anti-quated arms, divided into groups that warred against each other as much as the government. But they had managed for several years to kidnap for ransom high government officials, diplomats and businssmen, murdering a number of them in the process. They could also claim a number of direct assassinations.

Despite Cuban efforts to "export" revolution and a surge of guerrilla activity in neighboring Guatemala in the 1960, the Salvadoran left had remained largely nonviolent until the end of that decade, consisting primarily of the aging stalwarts of the Salvadoran Communist Party, remnants of the 1932 "Bolshevik revolution."

Many Salvadoran guerrilla fighters date their radicalization from the 1972 overturning of the election results. The military government closed the national university and banned student organizations and convinced many that clandestine fighting was the only route open to them.

But the Salvadoran guerrillas still had a long way to go. A group of Marxist union leaders who broke away from the pro-Moscow Communist Party, bolstered by newly disgruntled student members, named itself the Popular Forces of Liberation, Farabundo Marti(FPL), after the peasant leader of the 1932 uprising. Another group of students and disenchanted young politicians, believing the FPL strategy of longterm popular war, led from the rural hills into the urban areas, to be too slow, formed Popular Revolutionary Army (ERP).

The ERP, led by Ernesto Jovel, local student poet Roque Dalton, Joaquin Villalobos and Ferman Cienfuegos, placed a heavy emphasis on strict militarism and quick results. Through a series of kidnapings for ransom of prominent businessmen, it quickly amassed a heavy warchest.

Those same tactics, however, caused tensions among its large leadership and, in 1975, after a "popular trial," Dalton was executed by the group for "treason." As a result, Jovel and Cienfuegos broke off to form their own guerrilla group, the Armed Force of National Resistence (FARN), which stressed the need to organize and indoctrinate the masses before calling them to insurrection.

Each of the three main guerrilla groupings spent the next several years harassing the military and economic power structure. Each was known for a particular type of revolutionary tactic -- the FPL for targeted political assassinations, the ERP for bombings and, along with the FARN, kidnapings. At the same time, each promoted for formation of its own coalition of union and peasant organizations that could hold the front, and public line, against the government through strikes, propaganda, protest demonstrations and peaceful embassy occupations.

Although the Sandinista victory in Nicaragua in July 1979 convinced the guerrillas that outright leftist victory also was possible in El Salvador, they continued to disagree bitterly on tactics and strategy. At the same time, the Nicaraguan success persuaded Havana, which had largely ignored the Salvadoran guerrillas except for occasional training in Cuba itself, to lend them an organizational hand.

That decision and the October coup in El Salvador would reach forward into the Reagan administration. Within a week of the coup, the guerrilla factions all had declared all-out war against the new junta.