In its first week in office, the Reagan administration trumpeted a bold departure in foreign policy for America. The president warned that international terrorism would be met with "swift and effective retribution," and Secretary of State Alexander M. Haig Jr. warned that action would also be taken against the "terrorist governments" of the Soviet dnion and its "Cuban proxy."

"International terrorism will take the place of human rights" as a priority in the Reagan administration, Haig added, "and it's time that it be addressed with greater clarity and greater effectiveness by Western nations and the United States as well."

The message was clear, and in its first phase brought no sharp demur from American public opinion or allied governments. Jimmy Carter, through the emphasis he placed on human rights, had made thhe United States look soft against the Soviets, in the words of one new official. President Reagan would show that he knew where to "draw the line."

In what the official described as a "fortuitrous combination of coincidences and circumstances," a specific crisis already was under way in which Reagan could demonstrate his resolve -- the ongoing attempts by leftist guerrillas to overthrow the U.S.-backed government of El Salvador. It was from that steamy, little-known Central American republic that Reagan, White House press secretary Jim Brady said recently, would "send a message to Moscow."

Haig launched what Carter's human-rights specialist, Patt Derian, later would call "a political blitzkrieg" in mid-February by dispatching his top European affairs aide, Lawrence Eagleburger, to tell U.S. allies that El Savador had become a test of Western solidarity. The administration charged that Cuba was arming the left there. The mission produced mild disquiet in some capitals, but was by and large welcomed as a reassuring sign of a new American assertiveness on the world scene.

French President Valery Giscard d''Estaing for example, said in a private conversation on Feb. 20 that he would have no problem with an active American role in a region on Washington's doorstep, and Reagan could count on French support as long as the conflict was not escalated into a global and public challenge to the Soviets.

Within hours of that remark, the administration appeared to many Europeans and Americans to have done just that by letting it be known to the press that at a private briefing to foreign ambassadors in Washington, officials had said that the administration's "most urgent objective" was to stop the flow of communist arms to Salvadoran guerrillas and to "go to the source" to stop the arms.

Those comments, delivered by Haig's deputy secretary, William P. Clark, clearly were intended to leave the impression that Reagan was ready to stage a 1980s version of the 1962 Cuban missile crisis confrontation with the Soviet Union unless his demands on El Savador were met. Public reaction this time was quick, and sharp, with both liberals and conservatives suddenly raising the question of whether El Salvador was worth those kind of stakes.

At the same time, some officials in the government and on Capitol Hill have begun to question whether the evidence the administration has presented - an inch-thick compendium of alleged leftist documents uncovered by Salvadoran security forces -- proves that the involvement of a "worldwide communist network" in El Salvador is an extensive or threatening as the administration says.

Haig has proposed to counter the "massive amount of arms received by the left with the shipment of $25 million in U.S. military supplies and an initial 57-member contingent of U.S. military personnel. Yet, according to one Pentagon source, the "200 tons" of weaponry the guerrillas are reported by the documents to have received is a "spit in the bucket" that "a company of soldiers -- 200 troops -- could go through in a week."

Other officials have questioned the State Department's descriptions of guerrilla strength and of Salvadoran government requests that have conflicted with accounts coming out of El Salvador itself.

In the last week, administration officials have begun to take a somewhat different tack. Deemphasized as the showpiece of the newly tough United States, El Salvador is no longer cited as the first example of how Reagan is different from Carter. In fact, the officials stress, if anyone should be credited with current U.S. policy in El Salvador, it is Carter.

"I didn't start the Salvador thing," Reagan said somewhat defensively at his news conference Friday. "I inherited it." And in any case, he noted, while the previous administration campaigned with warnings that Reagan would be a threat to peace, "they were doing what we're doing" in El Salvador, "sending aid . . . of the same kind we're sending."

This sequence of events has done far more than rivet the nervous attention of American citizens and foreign leaders on Central America's smallest and most heavily populated country. It has demonstrated a certain style of decision-making within the new adminstration that is likely to be an important feature of its future dealing with the rest of the world. And it has cast into bold relief the policies of the Carter administration that Reagan came to office denouncing and that he now says he is carrying out, in one country at least. The question is whether or not those policies are likely to work any better for Reagan than they did for Carter.

El Salvador was the stage on which Jimmy Carter would give perhaps his most anguished version of Hamlet as played by a policymaker.

In the last, frustrating year of his presidency, he did on some days favor military involvement of the kind and scale Reagan has brought into being. This was the Carter who ordered a U.S. military team into El Salvador to mount "Golden Harvest," an operation in which the Salvadoran military command was able to halt guerrilla plans to destroy the annual harvest of cash crops.

On other days, however, according to officials who worked with the White House on this problem, Carter looked at plans for increasing the number of military advisers the United States would send to the increasingly messy insurgency and would seem to recall both the approaching November election and his prideful assertion that no American lives had been lost in combat during his administration.

"Carter just decided not to do it," one such official said. "He had a tendency to blink at critical moments."

The problem that most bedeviled Carter was the one that in the final analysis probably will pose the key test for Reagan's assertions of continunity in policy when it comes to dealing with El Salvador: whether to link U.S. military aid, which the Salvadoran military establishment wanted but the civilians on the junta were less certain about, to the social and political changes the civilians were pushing but the military leadership was stonewalling.

Reagan refused at his press conference Friday to rule out a continuation of military aid if the military takes complete control of the government, breaking with the kind of linkage that Carter had insisted on, at least in public.

This vagueness is beginning to drive a wedge between the administration and members of Congress who are sympathetic to the idea of cutting off shipments of arms from the outside but who wonder about the priorities that are being placed on getting U.S. military advisers into El Salvador.

"The Reagan administration claims to be committed to the same course, but appears to be much more open-ended in its commitment to the junta than Carter was," Rep. Stephen J. Solarz (D-N.Y.), said. "There is an implicit repudiation of linkage of reforms and aid, and this is particularly strange coming from an administration that insists that linkage is the key to our own relations with the Soviet Union."

That same lack of linkage of American help to political solutions is increasingly bothering European allies. European officials who met with Haig and his aides in the week following the disclosure of the willingness to "go to the source" came away convinced that the crisis in El Salvador has crystallized in a small inner circle of decison-makers within the State Department who give priority to a hard line in East-West relations over regional aspects of foreign policy problems yet to come.

In that circle, these officials said, are Policy Planning Director Paul D. Wolfowitz, an expert in strategic arms limitation negotiations; Counselor Robert C. (Bud) McFarland, former military assistant on the National Security Council; Richard Burt, former New York Times reporter who is now head of Politico-Military Affairs; Eagleburger and one or two others. Clark is directing the special group dealing with El Salvador.

Thus far, however, there is no sign that Haig is encountering significant dissent to his policies from the regional specialists who have been held over from the Carter administration. In his bid to win congressional support, Haig is said to be assuring conservatives on Capitol Hill that those officials have "done a 180-degree turn" on El Salvador.

Even so, Haig's nomination of Thomas O. Enders to head the department's Latin American affairs bureau is likely to be held hostage by Sen. Jesse Helms (R-N.C.) in an attempt to trade approval for promises by Haig to go slow on the land reform and economic changes in El Salvador that have infuriated Helms. "This is no place for on-the-job training," a Helms associate said.

The effort by Carter to hold together a linkage approach to El Salvador came apart in one tragic week last Novmeber, shortly after his own crushing defeat at the polls. On Nov. 27, six nonguerrilla politicians, leaders of the opposition Democratic Revolutionary Front, were kidnaped and killed in San Salvador by men the embassy believed had at least the protection, if not a direct link with, government security forces. Less than a week later, in an action that first focused the attention of most Americans on El Salvador, four American churchwomen disappeared while driving outside the capital. Their bodies were found three days later, with strong indications that the security forces again were involved.

Those events broke open problems that had existed for El Salvador's shaky coalition since its first day of existence, Oct. 15, 1979. And as the following weeks would show, they were problems that swirled not only through San Salvador's cool, high-ceilinged Presidential Palace, but also through the hallways of the Washington policy-making bureaucracy.

The bloodless coup that put the coalition in power had gone off without a hitch, as a group of liberal young Salvadoran Army officers, simply informed then-president Carlos Romero that he and his aides would be leaving. Himself a somewhat faceless general, Romero was the latest representative of a system that for half a century had ruled a downtrodden peasant majority through feudal landownership.

In addition to two "progressive" Army colonels in the new junta, there were a civilian businessman and a Catholic university rector who was known to be among the strongest critics of military human-rights abuses. To round out the five-man junta, they added Guillermo Ungo, a social democratic politician whose 1972 vice presidential victory had been blatantly stolen by the armed forces.

For the Cabinet, the military insisted only on retaining control of the Defense Ministry, while other posts were filled with civilian political activists, liberal technocrats and even members of the local communist-front party.

All appeared to agree that the new government's goals were three -- to end repression by government security forces, change the country's inequitable social, economic and political structures and prevent the left from taking over.

It was only a matter of weeks, however, before the weight of El Salvador's past, as well as its present, began to chip away at what began as a marriage of happy convenience. Although the goals might be the same, the priority, timetable and strategy for achieving them were not.

The arguments within the government tended to go in circles. As long as the military threat from the left persisted -- guerrilla effots to infiltrate and mobilize towns and villages and near daily armed strikes against armed forces installations -- it was difficult to rein in the government troops. Yet, the civilians argued, as long as the troops continued to rampage, indiscriminately killing citizens while seeking subversives, the population would continue to distrust the government and be open to the left.

Immediate and extensive reforms, as promised, were also vital to gaining popular confidence in the government, the civilians argued. Yet a powerful minority in El Salvador, those who owned the large plantations designated to be expropriated under land-reform proposals, and those who ran the banks to be nationalized, wanted no reforms to at all.

Many in the military, which as an institution had traditionally enjoyed a symbiotic relationship with the economic oligarchs that kept both groups in power, wanted to go more slowly with the reforms, or scrap them altogether.

In the first four months following the coup, the only thing that changed for most Salvadorans was that more of them died in politically motivated warfare including the guerrillas, the military and free-lancers who sold their services to the highest bidder.

By early January, all civilians in the government had resigned, protesting what they charged was continuing military repression.

Less than two months later, many of them also resigned, again charging that the armed forces were out of control.

Jose Napoleon Duarte, the populist Christian Democratic leader who had recently been allowed to return from seven years exile in Venezuela, was made a junta member. Ironically, Ungo had been his running mate when he won the 1972 presidential elections that the military overturned.

In Washington, policy-makers and analysts in a dozen different government departments were undergoing similar debates. While the U.S. military relationship with the Salvadoran government had been severed amid charges of human rights abuses early in Carter's term, many officials -- particularly in the Defense Department -- argued that it should be reinstated as a show of confidence in what was still largely a military regime.

Advisers in the National Security Council and a number of Latin American experts in the State Department agreed. "Military assistance is an essential component of any strategy in El Salvador," one official said recently of the debate at that time. "They are the center of power, and most of what you want, you have to get from them or with their approval."

Unless the Salvadoran armed forces could be offered a carrot in the form of a military relationship with the country that had long been their mentor, they might continue to balk at taking a firm hand against human rights abuses.

While others within the administration argued that the Salvadoran government -- meaning the military -- had shown no great sincerity in its efforts to stop repression and thus deserved an ongoing stick rather than a carrot, the case for military aid was bolstered by Defense and the CIA, of growing guerrilla strength and increased Cuban involvement in training and advising the left.

Several of the lefist groups had also announced the formation of a coalition to fight the government, an ominous sign indicating strength among previously bickering factions.

Listening to both sides, Carter opted for a compromise. In December, the White House sent to Congress a request for a small military training program, with no equipment included, designed to make the Salvadoran military more efficient and humane.

At the same time, he accepted, in theory, a proposal drawn up by the State Department policy planning office to send $50 million in economic aid to the Salvadoran junta, along with up to $7 million in military sales and credits and 36 U.S. Army advisers.

In exchange for the military aid, the department asked for immediate implementation of the still-languishing agrarian reform and bank nationalization programs. After extensive negotiations with junta member Col. Jaime Abdul Gutierrez and Defense Minister Jose Guillermo Garcia and his armed forces associates, a deal was struck.

In Washington, however, priorities had changed. The president who carried a human-rights banner "wasn't that comfortable at any time with military aid," one official said. In addition, when word that the program was under consideration had leaked to the press, a number of influential Democratic congressmen had personally protested, and Carter had received a letter from San Salvador's powerful archbishop, Oscar A. Romero, a leading human rights activist, urging that all military aid to the junta be stopped.

Guerrilla action at the time was steadily increasing and appeared to have shifted from urban areas to the countryside, where leftist leaders hoped to establish small zones of "liberated territory" from which to launch a coordinated offensive. Many of these areas, from which peasants fled in fear of what was to come, became virtually off limits for the armed forces.

In San Salvador, however, Carter had installed a new ambassador, Robert White, who disputed most of the CIA and U.S. military claims that Cuba and Nicaragua were materially aiding the leftists. White brought in a new intelligence staff and strongly disagreed, through cable channels to Washington, with what he said in congressional testimony last month were "frequent" recommendations by the embassy military group to send in U.S. advisers.

"The intelligence community in Washington and their representatives in Central America," White testified, "were on a constant state of alert to find any evidence of armaments coming in to support the guerrillas." Until recently, he said, "there was never any convincing evidence of this.

"I think that there is a driving need, which I do not pretend to understand, by the American military to involve themselves on the ground in Central America."

State Department Latin American chief John Bushnell has briefed a number of congressional committees and testified as often as White, whose figures and analysis of the Salvadoran situation he consistently disputes. The United States, Bushnell points out, sent no guns or bullets at all to El Salvador between January 1977 and January 1980. It was the Communists who started the escalation of armanaments, Bushnell said last week.

At the same time, Bushnell said that the Salvadoran government "is trying very hard to bring [military abuses] under control" and promised reforms are well under way.

White testified that on Jan. 19, the last day of the Carter adminstration, the head of the embassy military group asked his approval to send the Pentagon a request for immediate dispatech of 75 U.S. military advisers to El Salvador. "I asked him how he could possible justify presenting me with a message that would totally change U.. policy on the eve of a new administration," White said.

"He told me there was severe pressure from the Pentagon and from Southcom [the U.S. military Southern Command headquarters in Panama] to have this message before the new administration," White testified. "I refused to let it go out and explained that my whole purpose over the past four or five months was to work to keep the situation in such a way that the new administration would have time to consider what choices it should follow in El Salavador."

But despite White's concerns, and Carter's sporadic efforts to place his Central American policy emphasis on right rather than might, a number of decisions placing the Pentagon on the ground there were already made for Reagan.

As early as last spring, the Carter adminstration was taking some of the intelligence -- and pressure from the U.S. military -- seriously enough to begin substantially hedging its bets on peaceful reform in Central America. With little public or congressional notice, the focus of U.S. military activity was switched to neighboring Honduras -- a country with little or no domestic guerrilla movement, a relatively peaceful military government in transitiion to civilian rule and long borders with both Nicaragua and El Salvador.

It was along that border that the guerrillas had established some of their most impregnable strongholds -- entire communities that gradually were emptied of their fleeing population, which poured into refugee centers in the Honduran hills.

In the spring, an administration proposal to send $5.7 million in "nonlethal" military transportation and communication equipment was hotly debated and finally approved in Congress. Little attention was given at the time to another section in the same proposal authorizing $3.5 million in military aid to Honduras, including "$555,000 to equip and support units patrolling Honduran border areas . . . $2 million to equip and support one engineer batalion and $354,000 towards the purchase of miscellaneous equipment" such as "Marine communications, small arms and patrol boats."

Also included were at least 10 U.S. helicopters, with U.S. military trainers, and $620,000 to pay the personnel and upkeep of the equipment.

During public hearings last March, a Pentagon spokesman testified that the equipment was needed because "Honduras plays a key role in the movement of men and material to El Salvadoran insurgents. The Hondurans believe," said Pentagon official Franklin D. Kramer, "and our intelligence agrees, that their territory is being used as a conduit for men and weapons into El Salvador by insurgents with Cuban support, and they are also concerned that should El Salvador fall to the extremist left forces, Honduras will be among the next primary targets."

According to military sources in Honduras, 54 U.S. military advisers arrived in that country to give four-to-six-month training programs in rural counterinsurgency between July and December. Sixteen more advisers on a rotating program, the sources said, arrived last Jan. 15.

Some U.S. officials dispute the purpose of the buildup, maintaining it was designed to facilitate U.S.-Honduran coorperation in resupplying the Salvadoran military in the event of a large-scale insurrection, to facilitate the shipment of arms to the Salvadoran government from third country sources across Honduran territory and to prevent the use of Honduran border areas by Salvadoran guerrillas seeking safe havens.

A similar scenario was presented last November in a so-called "dissent paper," allegedly written by anonymous administration officials opposed to the Carter policy and widely circumlated in Washington. Although administration officials at the time discredited the document, as does the Reagan State Department, one high-level source from the Carter administration now says that the information in the document was "essentially true."

By fall in El Salvador, both the political and military battle had sharply escalted. Bickering guerrilla factions had announced their unification under the banner of the "Farabundo Marti National Liberation Front." Ungo's social democrats, dissident Christian Democrats and a wide assortment of political, union and professional groups had formed their own coalition and joined the guerrilla command in an umbrella "Democratic Revolutionary Front," headquartered in Mexico.

But it was a rapidly unfolding series of events at the end of the year, beginning with Carter's electoral loss, that sent his often conflicting carrot-and-stick policy into a virtual roller coaster ride.

Just after Reagan's electoral victory in early November, the Salvadoram guerrillas announced they were preparing for an all-out offensive that would present the new American president with a &ifaint accompli&n of leftist control on inauguration day.

While few in the U.S. Embassy in San Salvador took the threat seriously on its face, it coincided with new intelligence that former naysayers, including White and U.S. Ambassador to Nicaragua Lawrence Pezzullo, began to take seriously.

Newly obtained intelligence photographs, captured witnesses and a group of documents obtained in a raid by Salvadoran security forces on a guerrilla safehouse all pointed in the direction of newly coordinated arms shipments from Soviet Bloc countries into Cuba and through Nicaragua to El Salvador. Once again, debate picked up within the administration over an increase in U.S. military aid to El Salvador.

It was then that the killings of the six politicians and the American churchwomen stopped the debate in its tracks.

Although Carter immediately and angrily suspended all U.S. military and economic assistance to the Salvadoran junta while the deaths of the Americans were under investigations, "reform" of the security forces was quickly overtaken by the need to counter leftist revolt -- the declaration of a "final offensive" against the junta and the launching of a series of coordinated guerrilla attacks on Jan. 10.

While the guerrilla offensive was quickly defeated, Reagan entered office on Jan. 20 with a $10 million program of "lethal" U.S. military aid to the Salvadoran armed forces well underway, a packet of captured documents indicating communist weapons shipments to Salvadoran guerrillas and a Carter-written plan to send additional U.S. military advisers there lying on his desk.

Ironically, and perhaps more conveniently than is comfortable for many who served in the Carter administration, those programs, plans and documents reflect what the most conservative of Reagan's foreign-policy advisers long ago warned of and programmed for in El Salvador.