Arias's Job Well Done

IN the same month, Violeta Chamorro has taken office as president of Nicaragua and Oscar Arias S'anchez has left the presidency of Costa Rica. Mrs. Chamorro's work just beginning was made possible, to a significant degree, by Mr. Arias's just ending. Four years ago Arias took the reins of his small Central American republic and proceeded to do what no leader in the region had attempted before: Craft an indigenous diplomatic solution to the wars afflicting his neighbors. He insisted that peace couldn't come before democracy, nor democracy before peace. The two were intertwined, in his view, in a process that included mechanisms like free elections.

Arias was able to assemble fellow Central American leaders - people with such contrasting philosophies as Duarte of El Salvador and Ortega of Nicaragua - and get them to agree on a plan. But he recognized that the United States, too, had to be brought along. And his peace efforts often ran head on into the Reagan administration's contra-aid program. More than a few US foreign policy planners became annoyed with the single-minded Mr. Arias.

The Costa Rican never flinched at Washington's disapproval. He frequently attacked US backing for the Nicaraguan rebels as a hindrance to democracy. He once refused to meet in private with the CIA's William Casey, determined to keep his dealings in the public view and maintain his standing as an honest broker in the region.

The Arias plan opened the way for this year's startling vote in Nicaragua and the peaceful transfer of power there. Long before this result was in sight, in late 1987, President Arias was awarded the Nobel Peace Prize.

Some in Costa Rica have criticized Arias for not paying more attention to his own country's deep economic problems. Increased peace in the region, however, should help Costa Rica, as well as its neighbors, find greater prosperity.

Costa Ricans themselves have little doubt about their outgoing chief's accomplishments. Their constitution limits presidents to a single term. Otherwise, judging from public-opinion ratings, his reelection would have been a breeze.