Thirteen months after the Reagan administration began wading step by step into deeper military and political involvement in Central America, the problems of the region appear to be more serious than ever.

The civil war in El Salvador is more intense, and the political situation more uncertain as elections approach. There is little indication that, at their current level, U.S. efforts can turn the tide in favor of the Salvadoran government. And here at home, steadily growing opposition to U.S. policy in the region casts a shadow over administration options.

The stakes in Central America, as outlined by the administration, extend far beyond the borders of war-wracked El Salvador. At the northern end of the isthmus is Guatemala, "strategically the most important Central American republic because if its size, population and raw materials, oil included," in the words of Secretary of State Alexander M. Haig Jr. Guatemala is "clearly the next target" of revolutionary forces, Haig said in an interview. And, "if you go from Nicaragua, to El Salvador, to Guatemala,...the run into Mexico is a very short one."

Although Haig avoids referring to "dominoes," because of the echoes of the Indochina debate, he clearly sees them as teetering in both directions in Central America, through economically troubled Costa Rica as well. A senior aide to Haig said that Cuban-backed leftists in Nicaragua "could walk across Costa Rica without much trouble and into Panama," thus threatening the Panama Canal.

The region between the Mexican oil fields and the canal, Haig said, is "a hinge area for vital American interests." Beset by social and economic woes, it is threatened by "alien ideologies for revolutionary change" that he described as loyal to Cuba and the Soviet Union. President Reagan, in a speech last week, described the Caribbean Basin as "a vital strategic and commercial artery" for U.S. trade, imported oil and strategic minerals.

Yet, despite the high stakes, what appears to have been missing in the year-long evolution of administration policy-making toward Central America is a well-defined strategy in pursuit of clear and agreed objectives. And like the decisions regarding stepped-up U.S. involvement in Indochina in the early 1960s, there is no evidence of precise calculations of the risks to be accepted or the resources to be expended in the long run for what is essentially an open-ended commitment.

The Reagan administration inherited a region in trouble and a policy in flux. On Jan. 10, 1981, leftist guerrillas in El Salvador launched a bloody but unsuccessful "final offensive" in an effort to win a quick victory before Reagan took office Jan. 20. In response, President Carter, in a sudden reversal at the 11th hour of his presidency, authorized the emergency dispatch of military assistance to the beleaguered Salvadoran government, including the first "lethal" weaponry and U.S. military instructors.

To a new administration already disposed to view the problems of the region through a military lens, the "final offensive" presented a need for immediate military decisions. It supplied, as well, dramatic reinforcement of the belief of the incoming policy-makers that support for subversion by Cuba and Nicaragua is at the center of the region's woes.

Moreover, the suddenly altered circumstances in El Salvador, coming before any other test from abroad, provided Haig and some others with an immediate chance to "draw the line" against communism under seemingly favorable circumstances in the backyard of the United States.

In an examination of this year of policy-making, it is Haig who emerges as the key figure. He led the campaign in the early weeks for "going to the source" of the trouble, Cuba. Later he presented plans including deployment of U.S. military forces to stop the flow of armaments to and from Cuba. Still later he was the author of a regional approach to the problems.

While Haig throughout appears to have urged tough stands, the White House and other agencies, including the Defense Department, have alternately circled, approached, and stepped back from his positions, according to their own views of what was happening in Central America and how it could affect other priorities.

The first weeks of the Reagan presidency were a period of extraordinary activity regarding Central America. It was the first issue from abroad to demand decisions from the new administration, the first to activate the telephone lines and to bring urgent cables from a foreign capital clattering into the State Department operations center.

In those initial weeks, Haig, anxious to assert control of the decision-making process, moved quickly to display mastery and toughness as well as an outspoken anticommunism that seemed in keeping with the new president and his strongest supporters.

On an operational level the administration soon authorized $25 million in new emergency assistance to El Salvador--five times what Carter had provided--and dispatched more U.S. military instructors to a total of 55. Additional sums of both military and economic aid were proposed for the new budget year.

On the political level, Haig charged that El Salvador was the victim of a global communist campaign and threatened to "go to the source," meaning Cuba, unless it ceased. The State Department made the charges in briefings in Washington for foreign diplomats, flying trips to Europe and Latin America by high-level emissaries and a controversial "White Paper" entitled "Communist Interference in El Salvador," based largely on documents captured late in the Carter administration.

The traditional low profile of Central American problems had suddenly become high profile. What previously had been considered a local or at most a regional conflict now was seen as a global test of American power and resolve in the East-West contest.

"Before the new administration arrived, El Salvador policy had been controversial within the government, with the smell of failure on it from the beginning," said a career official who watched the developments. "You could say that the policy was an orphan, but in early 1981 it kind of got adopted."

Haig was seeking, he recalled recently, "to take quick action to take care of the problem, and that problem is Cuba and the Soviet Union." But as it turned out, his tough warnings aimed at Havana and Moscow had quicker repercussions at home, generating fears that the United States was about to go to war in an unknown land for obscure reasons.

Early on in the crisis, it was decided that problems with Cuba and Central America should not become "presidential," according to two senior Reagan advisers, who calculated that there was much political risk and little potential gain in the military and political crises of the region. At least until Reagan made his Caribbean Basin speech last week, the advisers said, they sought to minimize his public identification with the problem.

Despite this reasoning and these efforts, the potential effects on Reagan were demonstrated early last year. A tide of protests from aroused Catholic and other church groups and from the right, left and center of the domestic political spectrum poured into the White House over Central American policy. Richard Wirthlin, the presidential pollster, reported a sharp and sudden drop in presidential popularity. The White House high command wanted to keep the emphasis on the top-priority economic program then working its way through Congress, but "it didn't matter what we decided because El Salvador kept coming back," a senior adviser recalled.

There had been no decision at the White House, according to a participant in discussions there, to threaten war with Cuba. "The decision to hype it was external to the White House," according to this account. It was agreed that Haig would continue planning the policy to deal with the Central American problems, but he was instructed to cool the alarming rhetoric.

Looking back on those early months, Haig observed recently, "I said what I said, and there was no echo. In fact, there was a reaction." He quickly added, "But I wasn't wrong."

The spring was a period of calm in the developing U.S. policy toward Central America.

The Salvadoran guerrillas, who had been roundly defeated in their January offensive, had gone into a period of retraining and rethinking that would last six months. By late May, a senior U.S. official in Washington was describing the Salvadoran insurgents as "increasingly on the defensive" and limited to "nodules of very small guerrilla strength."

On April 1, despite acknowledgement that there had been "no hard evidence of arms movements through Nicaragua in the past few weeks," the State Department announced Reagan's suspension of the Carter economic support fund for the Sandinista government because of the earlier flow of arms.

The cutoff reduced U.S. leverage with Nicaragua but it appealed to adherents of the 1980 Republican National Platform plank that rejected aid to "any Marxist government in this hemisphere" and had specifically mentioned Nicaragua.

Despite the troubles they generated at home, by late spring the case was being made that the high-profile warnings had sobered the Nicaraguans and Cubans, altering the situation in the region.

Just as it began to look as though the administration had won a painless victory, word began to arrive through intelligence sources in June that the Salvadoran guerrillas were returning to the battle with new tactics. The small-scale but widespread attacks that followed, including the destruction of power plants and other economic targets, were taking a serious toll by late summer. "This called into question our assumptions up until that time," said a State Department policy-maker.

Intensified concern about Central America generated what was to be the second major cycle of policy-making. No early military improvement in the Salvadoran situation was in prospect, so the center of attention turned toward negotiations as a means of neutralizing the problems, especially on the Nicaraguan and Cuban fronts.

As one strand of this effort, Thomas O. Enders, the newly installed assistant secretary of state for inter-American affairs, was authorized to explore the possibility of a rapprochement with the Sandinistas. Beginning in meetings in mid-August in Managua, Enders secretly offered improved relations, and suggested an eventual resumption of U.S. aid in return for a cutoff of Nicaraguan support for the Salvadoran guerrillas and limitation of Nicaragua's own military buildup. But by October the talks had broken down under mutual suspicion of bad faith and intransigence.

In the meantime Haig discussed the problems of Cuba at length with Soviet Foreign Minister Andrei Gromyko at the United Nations in September. According to the account of the meeting by a well-placed administration official--an account that is vehemently denied by Haig--the secretary of state and the Soviet foreign minister discussed an arrangement by which Cuba in the American sphere and Poland in the Soviet sphere would move "to a closer relationship with their principal neighbors."

There is no sign, in any case, that a "spheres-of-influence" arrangement ever got off the ground.

With diplomatic discussions of the problem going nowhere, the floodgates of rhetoric opened in Washington. Haig attacked "mounting evidence of the totalitarian character" of the Sandinista government, and senior U.S. officials began speaking openly of the need to take action to stop the arms flow to El Salvador, thwart Cuban President Fidel Castro's activities in the hemisphere and specifically to prevent Nicaragua from moving further down the road toward becoming "another Cuba."

The tough language, it now is clear, coincided with a third phase of policy-making: consideration of a much more muscular American stand as outlined in a long-promised plan sponsored by Haig for U.S. action in the region. Although some reports say Haig submitted it to the National Security Council as early as August, it was not given serious consideration at the top level until the fall.

Details of the Haig plan are still unknown to the public, and Haig and others will not discuss it. The general outline is clear enough: a scenario beginning with direct warnings to Castro to mend his ways, followed by deployment of U.S. military forces sufficient to stop the flow of supplies to or from Cuba. It was recognized that additional U.S. military action could be required in the case of Cuban or Soviet opposition. Another facet of the proposal, it is believed, involved pressures against Nicaragua.

In discussing his ideas about Cuba earlier in the year, Haig told a caller, "You don't go in and invade. We have to put the pressure on up to and including cutting them off." He was convinced, he said, that the Soviet Union would not go to war unless the United States violated its part of the 1962 Kennedy-Khrushchev understandings, including that the United States would not invade Cuba. When his plans were completed, "we'll see who the tough guys are in this administration," Haig said.

Haig's plans for "moving battleships around" in the Caribbean, as one source described it, rang alarm bells throughout the top rank of the executive branch, especially at the Pentagon. Responses from Secretary of Defense Caspar W. Weinberger and other senior defense officials, it was reported, ranged from skeptical to hostile.

The Pentagon's reticence, according to officials, arose from both practicality and priorities. Such a plan, according to the career military, would require large-scale diversion of American forces from other areas considered more important. The Pentagon did not discount the dangers to the relatively unguarded U.S. southern flank of countermoves by Cuba and, though less likely, the Soviet Union.

For all the risks, it seemed uncertain that the U.S. activity would succeed in quashing longstanding guerrilla struggles in Central America, and there was even a chance that such intervention would trigger uprisings against U.S.-backed regimes. Moreover, such a costly and dangerous sideshow, in the military view, might well destroy U.S. public support for the Pentagon's main event, the major increases in defense spending, programs and readiness.

A series of National Security Council meetings to consider the Central American problems came to a head when Reagan, following anNSC discussion on Nov. 16, is reported to have approved a 10-point program for the region. The points included the long-promised Caribbean Basin economic proposal, new military aid and U.S. training for Salvadoran forces, improved intelligence and public-information activities, and tightened U.S. economic sanctions against Cuba.

Reagan last November made two decisions regarding the U.S. military, according to informed sources:

Improvement of the U.S. military posture in the Caribbean to demonstrate to Cuba, Nicaragua and others U.S. concerns and readiness to take action if required. Among the measures that followed were the establishment of a new Caribbean military command to coordinate communications and intelligence, discussions with Honduras and Colombia on U.S. access to improved airfield facilities, and repeated U.S. military exercises in the area as a show of force.

Development of contingency plans to deal with "unacceptable military actions" by Cuba. One set of the authorized plans covers the possible use of U.S. forces to deter the introduction of Cuban forces into Central America. Other plans involve possible use of "direct pressure" against Cuba, including a sea quarantine against importation of petroleum and retaliatory air strikes against Cuban forces and installations.

Perhaps the most controversial decision by Reagan was to start down the path of secret operations against Cuba and Nicaragua. According to the sources, Reagan approved a proposal to encourage and support foreign governments in political and paramilitary operations against the Cuban presence in Central America and Cuban-Sandinista backing for insurgency in the area. The NSC was considering a $19 million CIA proposal, whose status is unknown, for support of such activities--primarily involving non-Americans but possibly involving U.S. intelligence personnel in "unilateral paramilitary action against special Cuban targets."

A rationale for U.S. covert actions, according to an official who disclaimed any knowledge of Reagan's specific decisions, is that Cuba has been waging secret war against the United States through undercover activities, much as the United States acted against Cuba two decades ago. A background paper presented to NATO experts and sent to 50 U.S. diplomatic posts last October, and released publicly in modified form last December, reported that "Cuba has significantly intensified covert operations throughout the hemisphere." It cited examples from Jamaica, Colombia, Costa Rica, El Salvador and other countries.

Another justification for the secret activities is to interdict Cuban and Nicaraguan supplies intended for the Salvadoran or other insurgencies. However, there is a degree of ambiguity, according to informed sources, between this limited objective and the more ambitious aim of weakening the Nicaraguan government with an eye toward its eventual overthrow.

Some specialists on Central America have expressed concern that a program of secret aid to anti-Sandinista forces in Honduras or elsewhere could undercut centrist elements that remain in Nicaragua, thus guaranteeing the very result the U.S. fears--that the country will become "another Cuba."

An American with detailed knowledge said, "The Sandinistas may not know how to govern Nicaragua, but they're lean and hard, and good at intelligence. They probably have the exile groups penetrated. It'll make us look like horses' asses worldwide if they U.S.-backed undercover operatives get caught."

Haig's scenario for a showdown with Castro was not adopted in its toughest form by Reagan, according to information available. Nonetheless, the preparedness and contingency-planning measures approved by Reagan will place the United States in a better position to take direct military actions later, should the president decide to do so. And Haig, far from discouraged, indicates a belief that the rest of the government is buying his ideas, inch by inch, under the pressure of events.

In a fourth phase of policy, meanwhile, the administration is moving both publicly and privately to fashion alliances of nations in the region willing to cooperate with each other and with the United States. Such efforts are much more time consuming but less risky than a unilateral "quick fix."

Haig announced the U.S. intention to seek regional solutions at a meeting of the Organization of American States in St. Lucia in early December. The recently announced Caribbean Basin plan is an effort to generate regional cooperation in the economic field. On the military side, the instrument for potential regional action is the 1947 Inter-American Treaty of Reciprocal Assistance, the Rio Treaty, which was pointedly mentioned by both Reagan and Haig in recent addresses.

In January, El Salvador, Honduras and Costa Rica, with U.S. encouragement, formed a Central American Democratic Community to work together, and invited help from Colombia, Venezuela and the United States. The United States has stepped up its aid and military training in Honduras, a key country bordering on three trouble spots. From the south, Argentina is reported to be playing a role against leftist forces in Central America.

Although Guatemala's tarnished human rights efforts, and congressional resistance, continue to make a military relationship with that country's government difficult, Haig is hoping that Sunday's election there will improve the political situation enough to justify the beginning of U.S. assistance.

The objectives of the United States remain unclear. The aim of some elements of the government, according to an official immersed in the problem, is "to beat the communists," or at a minimum to halt new Cuban-Soviet gains in the area. Some other elements of the government, the official said, have a more easily defined if not more easily accomplished aim. It is "to get Central America to shut up and go away again" to the obscurity that it previously enjoyed in U.S. policy and consciousness. From all indications, this is unlikely in the months ahead.