The incidents occur with tortuous regularity, relentlessly reminding Argentines of a past they long to forget. A bomb explodes outside a political party office. A union organizer is abducted and tortured. A journalist is beaten on a busy downtown street.

All through its first year of restored democratic government, Argentina has been plagued with a subdued but persistent undercurrent of political violence. The attackers mostly have been shadowy squads of men who rarely have been captured or publicly identified. The principal targets, however, have been clear: human rights advocates, union organizers, politicians, social workers and students struggling to consolidate their work after eight years of military rule.

"This series of incidents, which have in common intimidation and fear, seek to test the strength of democracy," Interior Undersecretary Raul Galvan recently announced.

Since the beginning of 1984, authorities have reported about 40 bombings around Argentina, as well as at least 18 cases of persons detained, questioned and beaten by paramilitary squads.

There have been six cases of politically oriented armed attacks, and dozens of others of threats. In addition, authorities uncovered one serious assassination plot against President Raul Alfonsin and defused a bomb planted on the plane of former president Isabel Peron.

Government officials publicly describe the violence as isolated "residues" of 10 years of bloody conflict between extremists of the left and right. Interior Minister Antonio Troccoli has frequently attributed the trouble to "the unemployed manpower" of paramilitary squads responsible for thousands of abductions and assassinations under military rule.

Many politicians and human rights advocates, however, say the problem is more serious. The incidents, they say, represent a concerted campaign by organized groups on the right and within the armed forces to destabilize democracy and return Argentina to its "dirty war" of the 1970s.

"Since there is no control over these groups, they go on doing what they think is normal activity," said Emilio Mignone, the president of the Center for Legal and Social Studies, one of Argentina's most prestigious human rights organizations. "There is a doctrine and a mentality and an established procedure behind it. These people think they are fighting to prevent the country from falling into Marxism."

Many Argentine analysts say the nation's violent tensions are likely to increase in the coming months as Alfonsin's government nears a decisive confrontation with adversaries on the right and in the military over human rights cases. Another trigger could be ratification of a proposed treaty resolving a territorial dispute with Chile.

The year-old dispute over trials for human rights crimes intensified last month when the Supreme Court ruled that a federal civilian court could try nine former military commanders accused of directing repression.

The military's own judges earlier refused to carry out the trials, and otherwise fractious military leaders have united in opposing any sanctions against their former chiefs.

Even as the trials of military leaders begin in the coming two months, the Senate is expected to begin an arduous debate over the treaty awarding Chile control over three small islands at the southern tip of South America that nearly provoked a war between the two countries in 1978.

The settlement has already inspired a wave of violence by right-wing nationalist groups, and was believed to be the cause of a plot to assassinate Alfonsin when the president visited the interior city of Cordoba for a pro-treaty rally last November.

"These groups have been pushed farther and farther into isolation under democracy," said presidential adviser Dante Giadone, who pointed out that both the treaty with Chile and the trials of military commanders have been supported strongly by the public.

"They are desperate. And violence has always been their tactic."

The most serious threat, authorities say, comes from organized paramilitary groups who appear to have continued the military's violent methods of repressing and intimidating perceived political adversaries. While no deaths can be attributed directly to such activity, several persons have been wounded or have suffered property damage during the last year in attacks clearly intended to gather intelligence on political or social groups or to stifle their activity.

Some of the most celebrated incidents have involved members of the government-appointed commission that worked until September to investigate the thousands of disappearances during military rule.

The homes of the commission's representatives in the cities of Cordoba and Mar del Plata and the office of a commission member in Rosario were damaged seriously by bombs, and a charge exploded at a Buenos Aires television station in July as it broadcast a commission-sponsored documentary.

At the same time, a number of lesser known activists have been detained, beaten, interrogated and in some cases tortured by paramilitary squads. The pattern of these incidents is jarringly familiar to Argentines: Typically, heavily armed men in civilian clothes drag victims from the street into unmarked cars, blindfold them, and take them away for periods ranging from a few minutes to 10 days.

One typical case occurred late last October, when Lilian Perez, a local official of the populist Peronist party, was seized by at least four men traveling in three unmarked vehicles as she walked through downtown Buenos Aires.

Perez was blindfolded, taken to an underground garage and interrogated about the activities of party leaders. She said she was beaten and burned on the face with cigarettes.

Other victims have included Communist Party activists, four journalists, labor organizers and a group of young, Catholic Church-sponsored shantytown workers in the Buenos Aires suburb of Quilmes.

"There is no security in our country," said Perez's husband, Benicio Perez. He blamed the attack on "the same ones as always, those that use violence as a method of political intimidation."

Human rights group officials and some diplomats say that many violent attacks are sponsored or carried out by groups within the armed forces' still powerful intelligence services, and some evidence strongly supports their position.

In Rosario last August, for example, a commando group broke into the city court building and stole hundreds of documents relating to human rights investigations. At the same time, another group overpowered a police guard and removed evidence from a house that had been raided on a judge's orders days before.

The house was being used as a secret base for Army intelligence operations, official sources confirmed, adding that intelligence agents were known to have carried out the attacks.

Government authorities say members of an Air Force security force may have been involved in the planting of a powerful bomb on a jumbo jet scheduled to carry former president Peron to Spain last May, official sources said. The bomb was disarmed before takeoff, but no arrests were made.

One ranking government source conceded that sectors of the armed forces were believed to be behind some of the violence, adding that the democratic government could not easily control such activity.

"They're intimidated by the military," he said of Alfonsin's civilian ministers. "They prefer to negotiate with them when these things happen rather than act aggressively or publicly."

"The government has to act," responded Mignone. "If it can't establish control, the situation will only get worse."