Gen. Augusto Pinochet, beleaguered for more than a year by economic failure and political unrest, has become a defensive and increasingly isolated ruler, stalled in his ambitious plans to restructure Chilean society and more dependent than ever on his power base in the armed forces.

A decade of skillful politicking as Army commander, abetted by Chile's strict military traditions, has made Pinochet one of the most entrenched of Latin America's modern military rulers. As economic recession and political exhaustion have divided and broken three nearby military governments in the last year, Pinochet has remained unchallenged within his own armed forces.

But only two years after inaugurating a constitution meant to reshape national institutions, Pinochet has increasingly come to resemble Latin America's long lineage of personalistic dictators, politically reduced to the narrow margins of strong-arm power.

From a government known for the stability and technocratic rigor of its economic and political models, Pinochet's administration has grown unpredictable and uncertain, repeatedly turning to Cabinet reorganizations, policy reversals and emergency plans to confront short-term crises.

Once supported by a broad spectrum of union and business leaders, the government now is openly at war with industrialists, farmers and bankers whose loud economic complaints have gradually begun to shift to political dissension.

Where once a slow and structured political liberalization was planned to create a new, "protected" Chilean democracy, Pinochet appears to be turning again to military-enforced repression and a gradual estrangement from both the traditional political right and the conservative ideologues aligned with the military since its 1973 coup against Socialist Salvador Allende.

"He is reaching the point where accommodation with his political bases is very difficult, and he is losing the capacity of political negotiation," maintained a Chilean political scholar aligned with the opposition. "What we are seeing is a gradual retreat to the military bunker."

Although Pinochet, at 67, seems to have lost none of his interest and aggressiveness after 9 1/2 years of rule, Chilean analysts say he has shown an increasing defensiveness in recent months, focusing in many public statements on his perceived enemies and occasionally hinting at a sharp political turn toward populism or extreme nationalism.

"Today it is necessary to remember . . . the immense support the military government has received from the public, when some seem to have deliberately forgotten it," he said in a televised address this month in which he repeatedly threatened his opposition.

Twice in the last three months, Pinochet had been forced to acknowledge waves of coup rumors, which, he said last month, were planted by Marxists "trying to undermine the monolithic cohesion" of the armed forces.

Pinochet has always been opposed on political grounds by Chile's proscribed centrist and leftist parties, but government repression and a consumer-led economic boom in the late 1970s stifled efforts to organize any significant opposition.

What has changed that balance in the last year has been the defection of Pinochet's former supporters after the collapse of that boom and the government's strict free-market economic model, a program so aggressively implemented and fervently endorsed by Pinochet that it had become a symbol of his government.

Proclaimed an "economic miracle" only three years ago by some international bankers and conservative economists, Chile has crashed in the last 18 months into one of the deepest recessions in crisis-stricken Latin America. The national product dropped by 14 percent last year, unemployment rose to over 20 percent, real wages fell by 16 percent and bankruptcies reached record rates as businessmen struggled with one of the highest levels of private-sector foreign debt in the developing world.

Early this year, the government was forced to liquidate or intervene in the operations of a large part of the banking system and the country's two biggest business conglomerates to prevent their bankruptcy. The causes were complex, but officials now acknowledge that some of the government's fundamental measures were mistaken.

Four Cabinet reorganizations and four new economic teams in the last year have failed to reverse the general decline.

"The situation is paralyzed, the government is stuck in the mud," said Carlos Podlech, the president of the National Wheat Growers' Association and a supporter of Pinochet's constitution in 1980. "The crisis has stopped being purely economic and has become political."

Key economic organizations that supported Pinochet, ranging from the truckers' union and small farmers' associations to the National Chamber of Commerce, have grown increasingly critical of the uncertainty in economic policy and some have shifted to alliances with Pinochet's opposition.

In the key agricultural areas of southern Chile, long a stronghold of the political right, groups of farmers and businessmen issued declarations and organized a series of protests late last year denouncing government programs and demanding drastic changes in policy. Military authorities eventually were provoked to close two radio stations and break up one demonstration violently, expelling leader Podlech from Chile for two months.

As business and union leaders have defected, their traditional allies in Chile's political right have slowly begun to follow them, and what was once a broad progovernment coalition is now in open disarray.

"We thought for a long time that the government was going to act," said a principal leader of a rightist movement founded to support Pinochet's constitution. "But we've waited too long and things have gone too far and the action hasn't happened. The government has separated itself from the majority of the political followers." Only six months ago, the movement still firmly supported the president.

The public discontent has given Pinochet's traditional political opposition a new impetus. In the last four months, two multipartisan organizations have been formed to press for an accelerated return to democracy. They unite for the first time factions from the right to the socialist left.

The most important of the groups, a front including the Christian Democratic Party leadership as well as Socialists and former leaders of the conservative National Party, issued its first statement this month and soon will begin to issue alternative programs on the economy, political reform and even foreign policy, according to its leaders.

For months, politicians and journalists here have expected Pinochet to seek to strengthen his civilian political base by reshaping his policies to suit either the traditional right-wing democratic groups, who have called for political liberalization as well as economic reform, or extreme nationalists, who have asked for a political crackdown.

But Pinochet, hinting at both routes, has made no commitment. Instead, he has rejected the reforms and policy changes presented by both groups in private negotiations, according to political sources. He has further alienated right-wing sectors by postponing even those political steps called for by his constitutional transition program, concentrating instead on strengthening his authority in the armed forces.

That last political redoubt, by all accounts, is formidable. Despite the relatively rapid pace of the recent political shifts, opposition politicians seem to agree that without the overwhelming support of military officers no change will be possible in Pinochet's plans to hold office until 1989.

Chile's military, built on the traditions of the German officers who trained it before World War I, remains one of the most rigidly hierarchical and unpoliticized forces in South America.

Military officers, who until the 1973 coup had little tradition of political conspiracy, continue to respect the chain of command as the center of their institution. In a relatively compartmentalized society, they have little contact with civilian political or business leaders.

"This is the last Prussian army in the world," said one officer who recently retired from it. Over the last decade, Pinochet has concentrated authority in his position as military commander in chief and separated the bulk of the Army from both the government and any kind of political responsibility.

For the opposition, the military's position has become the focus of political strategy. Rather than seek to mobilize the country against Pinochet, many leading politicians say they are more concerned with creating conditions that would prompt the armed forces to act.

"The political sectors are less important for wearing down Pinochet than they are for preparing for the moment when he is worn down," said Manuel Antonio Garreton, a Chilean political scientist who is affiliated with a front called the Socialist Convergence. "What the political parties must do is show the armed forces that they can present a democratic alternative that seems responsible and viable."

For now, many political leaders suggest that neither alternative nor the degree of social disorder that would prompt a real threat to Pinochet in the armed forces exists. Many say that if economic conditions improve, the impulse for a democratic opening could evaporate.

Unless Pinochet is soon able to reverse the economic and political momentum, however, many observers here say he could permanently lose the power he enjoyed in the late 1970s. "The government could maintain itself indefinitely with short-term maneuvers and playing off sectors," one party leader said. "But it would not address the long-term issues. And if the country continues to slide, the situation could start to deteriorate very rapidly."