IN THE LAST five years, no friendly noncommunist nation has assaulted its citizens' lives and liberties more ruthlessly than has the military regime in Buenos Aires. Has the human rights condition there "improved substantially," as Secretary Haig says it has? What is to be made of the reception of the president designate of Argentina here?

The questions are worth asking if only to make the point that, for the sake of human rights and overall policy alike, the debate has got to be rescued from the abstractions and rigidities of the political trench warfare that has come to substitute for reasoned argument in recent years. And when you do look more closely at Argentina, you see a place that fits neither side of the old debate. You see a country that has passed through a nightmare of unofficial terror on the left and official repression on the right, and is trying now in its fashion to find its own, more acceptable national style. The ascent of Gen. Viola, who has been designated by his fellow officers to be the next president, is part of that effort: he represents the force of cautious, controlled relaxation -- the only kind of change feasible in Argentina.

Yes, Argentina's human rights situation has "improved substantially" in recent months. Not only did an ostensibly nonpolitical court manage to free some prominent arrested civil libertarians on the eve of Gen. Viola's arrival in Washington. The authorities, the State Department reported as he left, continue to release political prisoners, though perhaps 1,000 remain.No new "disappearances" -- summary political executions -- have been confirmed this year; there have been thousands in the past.

The administration many not have subtly designed its invitation to Gen. Viola as an encouraging nod to Argentine progress. But its hospitality will surely cheer many Argentines who wish to keep moving away from their country black past. Argentina is not the same place it was when Jimmy Carter entered the White House. A different sort of American human rights policy, one that happens to be consistent with the administration's security priorities, could be effective. Ronald Reagan, by not being perceived as a threat in Buenos Aires, has opportunities for quiet leverage that Mr. Carter never knew. Let us see how things go.