A REGENTINA AND CHILE have just done something brave and constructive. Rather than go to war over the Beagle Channel, which lies at the southern tip of their 2,500-mile border, they have agreed to submit their dispute to mediation by a representative of Pope John Paul II. Both countries have military regimes, and troubled regimes, and on each count the temptation surely was strong to play the nationalistic card and to posture, if not actually to fight. Yet they have committed themselves to seek a peaceful way.

The dispute itself centers on a handful of barren islands in and about the border (drawn in 1881) in the Beagle Channel. In the 1960s, Chile claimed some of these islands, Argentina objected, and they agreed to submit the question of the exact border to international arbitration. As the arbitration proceeded, the enflaming notion spread that the economic stakes might turn out to be immense, since the winner could draw a line out 200 miles to create an "economic zone," as many other nations were doing, and reap whatever oil and other minerals might eventually be found therein. When, after many years, the arbitrators last summer ruled for Chile, Argentina rejected their judgment. Its sensitivity to the resultant criticism presumably affected its readiness to accept papal mediation now. Chile, confident of its case, naturally preferred mediation to being invaded. Both countries, one suspects, were ready to be rescued from the excesses of their own pride.

The pope has more going for him than his moral authority in two heavily Catholic countries. His approach is different.The arbitrators addressed just the narrow legal issue of the border. The pope's mediator is empowered to address whatever other aspects of the issue, including access to offshore resources, he finds necessary to get the two countries to live as good neighbors. It is an intriguing experiment in peace-making. We hope John Paul II pulls it off.