The case of a pro-Nazi ex-intelligence agent who used to work for President Raul Alfonsin has become a serious embarrassment to the Argentine president, whose government has been at pains to put the right-wing extremist behind bars in connection with a series of major crimes.

The agent, Raul Guglielminetti, was on the payroll of the Casa Rosada -- the Argentine presidential residence -- when Alfonsin took office.

Military officials responsible for the president's security knew Guglielminetti and recommended keeping him on the payroll, saying he was an intelligence operative who could prove to be a useful informer, according to Dante Giadone, then undersecretary general of the presidency. So the government went on paying Guglielminetti, and he continued to report to work at the executive mansion.

He was later dropped from the government's employ, and now is under investigation for murder, kidnaping, theft and other crimes.

The Guglielminetti affair, front-page news here in recent days, shows the legal obstacles and investigative shortcomings that are frustrating the commitment by Argentina's democratic authorities to bring to justice right-wing "death squad" members who had free rein under earlier military regimes.

Despite convictions announced last month of several former military junta leaders for their roles as architects of the antileftist repression of the 1970s, the government is still widely perceived here as either reluctant or ill-prepared to move against lower ranking operatives suspected of carrying out murders, kidnapings and torture. The Guglielminetti affair has become a case in point.

At first, the administration appeared to go to considerable effort last year in having Guglielminetti extradited from Spain after he fled there. The one-time intelligence agent returned to Argentina in police custody on Dec. 24.

But last week a federal judge released Guglielminetti, saying the case for which he was extradited -- he is suspected of murdering textile industrialist Emilio Naum in June 1984 -- lacked sufficient evidence to hold him. The government prosecutor in the case supported the court ruling.

The release order has left many Argentines dumbfounded and has drawn exasperated allegations of government incompetence from human rights activists and some opposition politicians. Ricardo Kirschbaum, a senior political columnist for the newspaper Clarin, wrote that the episode has done the most to damage the political credibility of Alfonsin's administration since it took office.

Irritation and disbelief also was sounded two months ago when the Alfonsin administration could not manage to enforce arrest orders against six military officers and six civilians suspected of plotting against the government. Even a state of emergency, imposed in October specifically to facilitate detention of the 12 men, failed to secure the imprisonment of most of them.

After formally lifting the state of siege in mid-December and freeing the few alleged plotters being held, Alfonsin last week approved promotions for two of the accused officers.

Asked how the president could countenance promotions for men whom, only several weeks earlier, he had suspected of plotting to destabilize the country, Interior Minister Antonio Troccoli replied: "The investigation [of the alleged plotters] has not yet resulted in a judicial pronouncement. So until that verdict exists, they enjoy the full benefit of their rights."

Meanwhile, the 44-year-old Guglielminetti is showing every sign of relishing his role as a symbol of the far right.

No sooner had he been released from jail than Gente, a mass circulation magazine, appeared on newsstands here with a cover photo of Guglielminetti wearing a Nazi swastika.

The ex-presidential aide readily confirmed the authenticity of the snapshot, which he said had been taken while he and friends were "horsing around during a night of fun."

Answering questions from reporters, Guglielminetti praised Nazi ideology for having "set up an opposition to stop communism" and proudly defined himself as a "rightist but not a terrorist."

Such attitudes and bravura make Guglielminetti, for many Argentines, an archetype of the military and police operatives who carried out Argentina's "dirty war" against leftist dissent in the late 1970s and early 1980s.

"This whole affair is connected with the problem of the dirty war," said Giadone, who as former undersecretary general of the presidency had been Guglielminetti's superior. "He was an instrument, a tool of the others. You have to put him in this wider context."

Judges here continue to summon Guglielminetti for questioning in connection with the kidnaping of wealthy cattleman Ricardo Lanusse, a ransom of two $2 million for the kidnaped businessman Sergio Meller, the 1977 robbery of a currency exchange office, a swindle at the Gurruchaga Credit Cooperative and the kidnaping in 1983 of human rights crusader Guillermo Patricio Kelly.

Guglielminetti has been in and out of court and jail since he was 19 years old on various counts of theft, extortion and the illegal importation of arms. Authorities have linked him to the Argentine Anti-Communist Alliance, one of the paramilitary death squads that flourished during the dirty-war period.

By his own admission, he belonged to a "task force" that had committed "excesses" during this period. In 1978 he joined security forces attached to the presidential mansion. He was let go in March 1984 when the Navy captain who was Guglielminetti's main sponsor also left Alfonsin's staff.

Last May, police raided a summer house owned by Guglielminetti on the outskirts of Buenos Aires. They discovered there an arsenal of explosives, automatic rifles, napalm rockets, military uniforms and communication equipment said to belong to a right-wing death squad.