BUENOS AIRES -- The euphoria with which South Americans welcomed democracy's sweeping return earlier this decade has given way across the restless continent to frustration and disappointment with the results so far.

While popular support for democratic rule remains strong, public unhappiness with the way the new democracies are being managed has grown and begun to worry many inside and outside government.

The disaffection is more often heard than seen. It has yet to erupt, for instance, in sustained street protests or other violence. Evidence indicates both a general disenchantment with politics and a lingering fear of repression. But signs of discontent are clear in opinion surveys, national elections and conversations with workers, politicians, diplomats, journalists, academics and others throughout the region.

Hopes persist that the current democratic era will yet prove a historical turning point in a region long afflicted by swings between dictatorship and democracy. Yet the failure of the free systems to deliver the economic gains, social advances and structural changes initially expected of them has soured national moods from Ecuador to Argentina and eroded the standing of all elected governments on the continent.

"There was perhaps an excessively optimistic vision in the beginning about what democracy could do," said Marcelo Cavarozzi, an Argentine political scientist. "People are now discovering it cannot work miracles. Hopes have faded, the euphoria has disappeared."

In Argentina last month, voters forcefully registered their disillusion, handing President Raul Alfonsin's centrist party a stunning defeat in gubernatorial and congressional elections -- with the historically authoritarian Peronist party the winner. In Brazil, President Jose Sarney, a domestic hero last year for temporarily taming inflation, has become the target of constant disparagement as his government muddles through political infighting and the economy slows. Even Peru's 38-year-old populist leader, Alan Garcia, whose popularity rating hovered over 80 percent during his first 18 months in office, today draws approval from only a third of the population, according to surveys.

Amid such gloominess, scattered voices in letters to editors and elsewhere have started calling for a return to military rule. Democratic leaders have themselves been moved to concede renewed prominence to the armed forces -- in Sarney's case, due to a lack of civilian political support for his presidency; in Garcia's case, due to the spread of terrorist activity; in Alfonsin's case, due to uprisings by officers opposed to human rights trials.

Never confident of democracy's staying power, the region's armed forces still regard themselves as the ultimate saviors of their nations. They rank among those most disgruntled with the way things are going. Some officers in Ecuador and Peru, in particular, make no secret of their wish to retake power to restore a sense of order and stability.

Yet most South Americans, when asked, cringe at the thought of a revival of authoritarian government. Indeed, officials in Argentina, Brazil and Colombia are trying to broaden political participation and create more flexible governing systems as safety valves against the sort of discontent that has triggered coups before.

U.S. officials, whose encouraging winks and nods have been interpreted as green lights for military takeovers in the past, continue to make clear their support for today's insecure democracies. Quiet U.S. diplomacy may have been decisive recently in forestalling coup plans in Ecuador.

Even so, South American officials frequently complain that the United States and other industrialized countries have done too little to back up their verbal support for the fledgling democracies, describing Washington as obsessed with the conflicts in Central America.

U.S. authorities say budget cuts have reduced American options. "There isn't much we can offer, given current reductions in foreign aid and military assistance programs," lamented a senior Reagan administration official in Washington.

Ironically, by embracing democracy, South American states seem even more remote from Washington, with its focus on arenas of East-West struggle. But the battle for survival here remains a very real one.

It represents an important test of patience, mutual comprehension and common democratic interest between North and South.

Just eight years ago, only two democratic governments -- Venezuela and Colombia -- existed in South America. Today, only two military regimes -- Chile and Paraguay -- survive among the continent's 11 Latin republics. In Panama, the military wields power indirectly.

Some prominent South Americans such as Peruvian writer Mario Vargas Llosa contend that the current democratic experience is still the most promising the continent has ever known. Free expression has returned. Demagogic solutions to social and economic problems are out of fashion.

The new democrats have shown invention and sophistication in managing some crises. They also have stepped up the fight against the cocaine trade's corrupting influence in their societies, although with little impact as yet.

But most South Americans, while freer today than at any time in a generation, are also poorer. They remain handicapped by an oppressively large foreign debt, inefficient industries, bureaucratic mazes and gaping social inequalities, all largely inherited.

Argentina and Uruguay, the continent's two countries with the largest middle-class, are fighting to overcome years of stagnation just to climb back to income levels first reached a decade or more ago. Brazil, whose enormous resources and dynamism make it Latin America's most viable nation, is seeing its urban slums wracked by violence, its countryside unsettled by land conflicts and its health and education services decayed by neglect.

In Peru, an ominous Maoist insurgency has resisted all measures to contain it. In Bolivia, an astonishingly bold and painful effort to reorder the old tin-based economy still has far to go to lift the nation -- South America's poorest -- out of its perpetual state of crisis.

Even established democracies are under strain. Colombia, scene of ruthless drug barons, unyielding leftist guerrillas and sinister right-wing assassination squads, is convulsed by the highest incidence of peacetime violence in the hemisphere. Venezuela, its oil wealth diminished, is having to learn to live within tighter constraints.

Many had expected that the new responsiveness to popular wills would bring swift cures to enduring ills. South American officials blame themselves for fostering higher expectations than were achievable.

"People wanted to believe in miracles, but we should have conveyed a stronger sense of the difficulties involved," said Carlos Nino, a senior aide to Alfonsin. "Many are now saying we should urge people to be more realistic and recognize that no government can do much better under the difficult circumstances."

At the same time, politicians in the region face some tough policy decisions. Should the new democracies, for instance, concentrate first on spurring growth, containing chronic inflation or building up trade surpluses?

A recent report by the United Nations Economic Commission for Latin America concluded that the governments have pursued "see-saw" policies that have accentuated economic cycles and precluded solid and sustained growth. Noted the study, "Growth is not only modest but precarious in most countries, and promises to remain so."

Moreover, little democratic consensus has emerged on the type of economic system best suited to the crises at hand. In Peru, for instance, a surprise nationalization of private banks and insurance firms has provoked intense debate over whether government control or private enterprise is the key to economic development in an impoverished country.

Questions also have been raised about how to balance property rights against majority needs in a young democracy. In Brazil, legislators are wrestling with similar issues in a constitution-writing assembly, with no end in sight.

After decades of having been shoved to the sidelines, democratic parties often are still feeling their way in office, with sometimes self-destructive results.

The governing alliance in Brazil between the giant Democratic Movement and conservative Liberal Front parties fell apart in late September after months of strain. In Ecuador, a tug of war between conservative President Leon Febres Cordero and a leftist-dominated Congress has weakened the democratic process there. In Peru and Argentina, ruling parties are short of capable managers to run government ministries and state enterprises.

With a good part of their political capital already spent, national leaders are trying to recapture some of the credibility and public enthusiasm they enjoyed at their start. Brazil's Sarney, complaining of getting all the blame for what has gone wrong, issued a personal appeal this month for support in forging a new political pact. Alfonsin announced a new wage-and-price freeze Oct. 14 to stem Argentine inflation and retake the political offensive.

"You see a growing demand from all sectors for predictability and a firmer hand," said Alexandre de Barros, a Brazilian political scientist.