BUENOS AIRES, AUG. 12 -- Argentina's armed forces, after more than three years under civilian rule, continue to pose the most serious threat to democracy here, according to a report released today by the U.S.-based human rights group Americas Watch.

The study said the government of President Raul Alfonsin has undermined its own effort to prosecute military officers for crimes committed during the repression of leftist dissidents in the 1970s. Moreover, the report said, the authority and independence of the courts have been eroded by legislation passed in June protecting most officers from trial for tortures, abductions and murders during what is termed the "dirty war."

But the study also commended Argentine authorities for exposing the campaign conducted by security forces and said that on balance, "the recent Argentine experience is highly positive" and has produced "an increased awareness in large sections of society about the benefits of democracy and of tolerance for ideas."

The 88-page report, entitled "Truth and Partial Justice in Argentina," is the first by Americas Watch on Argentina since Alfonsin took power in December 1983, ending nearly eight years of military rule. Americas Watch is a nonprofit, private organization founded in 1981 to analyze and promote human rights in the Western Hemisphere.

"The main obstacle in President Alfonsin's path continues to be the military's resistance to the rule of law," the study observed. "Resistance to the judiciary is the only unifying factor today within the ranks, but it has been powerful enough to prevent any significant step toward an acceptance of democratic values.

"From what is known of their thinking, the officers who are gaining influence in the armed forces today are, if anything, more totalitarian and fanatic than the generation that took over the country in 1976 . . . . The fact that no significant democratic alternative to them is growing in those ranks is perhaps the greatest failure."

Although Alfonsin has cut military spending, dismissed dozens of top officers and introduced a new defense bill, his reform effort bogged down months ago over how to define a future role for the military under democracy. The Army's new chief of staff, Gen. Jose Caridi, has made public pleas for vindication of the "war against subversion."

Americas Watch leveled some of its harshest criticism at the so-called "due obedience" law, which has freed hundreds of officers from prosecution since June on the grounds they acted under orders.