Military Gets Foot in Political Door. Armed forces regain key role just as nation to vote for first civilian changeover in decades. DEJA VU IN ARGENTINA

NOT for 61 years have Argentine voters been allowed to change one elected president for another. Interrupting democratic rule again and again, the military has been a familiar player on the political stage. So it is not surprising that President Ra'ul Alfons'in is hailing next month's elections as a consecration of his country's fragile and besieged democracy.

But in what is supposed to be an entirely civilian affair, politicians are worried to find that senior soldiers keep appearing on the scene. And, of even greater concern, they seem to be calling the shots again.

``Factions within the Army are using the political situation to win more influence for themselves,'' says Miguel Angel Toma, one of the opposition Peronist Party's top military experts. ``The danger is they are trying to militarize everything.''

Recently, in a surprise move, the Supreme Court suspended indefinitely all trials of military officers facing human-rights charges. The magistrates cited technical juridical reasons for their decision. But others recalled that an end to the trials was one of the demands posed by rebellious Army officers during last December's military uprising.

The court judgment came on the heels of a presidential edict that critics say marks another step back by the civilian authorities.

The decree - broadening the armed forces' powers over domestic affairs - ``signifies the militarization of internal security, clearly weakening'' the police's role, complains the Permanent Assembly for Human Rights.

``It opens the door onto a past to which we do not want to return,'' the human-rights group adds.

President Alfons'in issued Decree 327 in direct response to the attack on an Army barracks last January by a maverick group of leftists.

The decree gives the Army the right to carry out domestic intelligence operations against potential ``subversives.''

Advised by a newly created National Security Council, on which all the military chiefs of staff have seats, Alfons'in has put the Army in charge of ``preventing the formation or activity of armed groups'' that might threaten the Constitution, as the decree puts it.

What worries human-rights activists is that the military's secret services be given the task of deciding who is a potential subversive, and who deserves watching.

Memories are still fresh of the repression unleashed by the military government in the 1970s, when soldiers routinely regarded any man with a beard as politically suspect.

Indeed, it was precisely to keep the military out of domestic security that Congress passed a Defense Law two years ago, specifically restricting the armed forces' role to defending Argentina from outside attacks.

``This new decree clearly contradicts the legislation we passed,'' argues Mr. Toma. ``It confuses the essential difference between defense and security, and if we give the armed forces an intelligence role in terrorism, they'll start spying on politicians, and then on businessmen, and then on the church.''

The military has clearly come a long way in restoring its influence since the generals returned power to civilians in 1983, humiliated by their defeat at Britain's hands in the Falklands war, and shamed by public revulsion at their appalling human-rights record.

President Alfons'in exploited that weakness to take a step unprecedented in Latin America: He put members of the former military juntas on trial for human-rights abuses. But having torn up the notorious Doctrine of National Security, which the Army had used to justify its repression, the new government did not offer the military a new doctrine to take its place, critics argue.

Army officers ``began to suffer from a terrible identity crisis, because they had nothing to do,'' once they had been stripped of their role as the country's rulers, explains military sociologist Jos'e Miguens.

Those frustrations have led to three military uprisings over the past two years, and on each occasion, the government's only response has been to make concessions.

Two months after Lt. Col. Aldo Rico seized an Army base during Easter week in 1987, the government sent Congress a ``Due Obedience'' law, lifting human rights charges against all but a handful of military defendants.

Two weeks after Col. Mohamed Ali Seineldin seized the same base last December, the armed forces won the pay raise he had sought. A fortnight later, the Army chief of staff resigned, as the rebels had demanded. And then last week, in apparent response to a third rebel condition for laying down their arms, the few human-rights cases still being pressed were suspended indefinitely.

Those successes have given the military a new power in society that politicians cannot afford to ignore. For example, Peronist presidential candidate Carlos Menem - the likely winner of next month's polls - found it advisable to visit army Chief of Staff Gen. Francisco Gassino as part of his campaign stump.

Lieutenant Colonel Rico told reporters he will vote for Mr. Menem, and Colonel Seineldin has told followers that if Menem outpolls his rivals but is kept from the presidency by a coalition of non-Peronist parties, he will ``seek to impose the popular will.''

General Gassino has discounted this blatant attempt to make the Army the arbiter of the election results, and has promised publicly that his service will remain neutral.

But, says military analyst Horacio Verbitsky, ``He knows the Army is the arbiter just by standing aside and keeping its arms crossed,'' because having found its way back to the center of the political stage, the military is a key player. And it is insisting on being treated as such.