Former Argentine president Isabel Peron, who has been under arrest ever since a military helicopter carried her away from the roof of Government House during the March 1976 coup that overthrew her government appears to be nearing release.

For the last few weeks, to mounting headlines and speculation in the Argentine press, the former president has been under medical surveillance in the chalet south of here where she lives under house arrest -- forbidden to leave, receive visitors besides her relatives and lawyer or participate in politics in any way.

She is reported to be suffering from an ulcer. Although this is not the first time Peron's ailments have surfaced publicly, there seems to be a deliberate effort this time to set the stage for what is to be perceived as the compassionate release of a fragile, 49-year-old woman.

It is generally assumed here that Gen. Roberto Viola wants Peron out of the picture when he assumes the presidency March 29. As a prisoner, she is an embarrassment to his public declarations of gradual democratization. As a free Argentine citizen, she might well present an intolerable threat.

She was, by general consensus, a disastrous president -- weepy, unstable, thougt to be strongly influenced by an astrologer who advised her on matters of state. But she carries the name and the vivid memory of her husband Lt. Gen. Juan Domingo Peron, the thee-time Argentine president whose death in 1973 thrust his widow, then vice president, into the nation's highest office.

The public working hypothesis behind this junta's political and economic policy is that they must undo the damage done by Gen. Peron if they are to "prepare" the country for a lasting democracy. But for all its fragmentation and vaguely defined politics, the once-powerful populist movement Gen. Peron spawned is still very much alive in Argentina, and some people think an active Isabel Peron might become a figurehead to unify the Peronists again.

So the main problem now seems to be deciding what to do with Isabel Peron once she is out. Late last December, the military junta members who deposed her announced that they were freeing Peron from "executive power" -- the authority they invoked when they arrested her during the 1976 coup. That leaves the former president at the dispostion of the Argentine court system, since she has four counts of fraud and embezzlement pending against her.

Those cases have proceeded slowly through investigations by federal judges, but Peron's attorney has argued that even if she should be found guilty of all four counts, she has already served enough time in detention. With her attorney reportedly maneuvering furiously and ducking interviews, and federal judges interviewing Peron yesterday at her home, the bargaining is said to hinge, among other things, on how long she would promise to stay out of Argentina.

It was assumed until recently that she would move north to Panama upon release. Two weeks ago, though, Panama's President Aristides Royo said publicly that although Peron had been invited to Panama, she probably would go to Spain.

The Perons lived in a Madrid suburb during Gen. Peron's most recent period of exile in the 1960's, and their old house there reportedly has been spruced up in recent weeks to prepare for Isabel Peron's arrival.

The rise to power and spectacular fall of "Isabelita," as she is called all over Argentina, is one of those episodes in Argentine history that seem scarcely credible to an outsider. Her nickname is a stage name, or so the stories went. Maria Estela Martinez, never formally educated beyond the sixth grade, is said to have begun calling herself "Isabel" during here career as a dancer.

She was working in a Panama nightclub when she met Juan Peron, the famous Argentine Army general who had been dumped from the presidency in a 1955 coup. She was 24, he was 59, and there are various romantic versions of the circumstances of their meeting.

They began living together, were married in Spain, and remained in the Madrid home while Gen. Peron courted the curious and the supporters who would help propel him back to power. The new Mrs. Peron was replacing the most fanatically adored woman in Argentine history, Eva Duarte de Peron, dead of cancer in 1952 at the age of 33, and even during those Madrid Years Isabel apparently embraced the ghost of her predecessor as fully as she could: It is said that when "Evita's" embalmed body was moved to the Perons' Spanish mansion in 1971, Isabel herself cleaned the corpse and combed its still-blond hair.

But Isabel never gripped Argentina the way Evita had. When Juan Peron finally came home in 1972, she tried. As she decended from the airplane that had returned them from exile, Isabel, wrapped in a white fur, was reported to say, "I swear that's the same white mink, or just like the same one, Evita always used to wear."

She was awkward in public -- nervous where Eva had been passionate, timid where Eva had been fierce. When she was chosen Peron's vice president making her next-in-command to a 78-year-old man, the Argentine public was incredulous, and not simply because no woman had ever held that position before.

James Neilson, a longtime resident of Argentina and political columnist, wrote in 1973, "should Peron die or be incapacitated, the vice president will automatically take over. With Isabel Peron as president, the chances of a military coup would be very great indeed."

That, of course, was precisely what happened. Juan Peron died nine months after taking office, and when the stunned period of national mourning was over, Isabel Peron began trying to assume control of a profoundly divided Peronist movement. Under her presidency -- and, her opponents believe, under the tutelage of astrologer Jose Lopez Rega, who was widely known as "the sorcerer" -- economic and political conflict escalated into such violence and hyperinflation that when the military took over in 1976, the most commonly expressed emotion here was relief.

On March 24, 1976, Isabel Peron met late into the evening with labor leaders at the baroque pink government building that overlooks the palm trees of the Plaza de Mayo. When the meeting was over, Peron went to the roof, expecting her regular helicopter escort to deliver her to her home in suburban Buenos Aires.

As they were in the air, according to later reports, the pilot said there were problems with the helicopter. The copter set down in the darkness at the municipal airport, and Peron was asked whether she would need any personal items before they took her away.