JUST AS THE strategic arms limitation talks have seen a certain licensing of the arms race, so the United Nations' Law of the Sea Conference, undertaken to find internationalist solutions to ocean issues, has seen an unprecedented extension of national claims to the seas. The territorial sea has been pushed out from three miles to 12 and in some cases to 200. States now claim control over the resources of their continental shelves as far seaward as they can exploit them. Many nations assert jurisdiction over coastal fisheries out to 200 miles. In this country legislation is pending to extend the equivalent of sovereignty to deep-seabed mining sites thousands of miles away. Whether this carving up of the oceans would have gone on anyway is a less important question than whether the process can be halted, if not reversed, at the session of the conference that opened this week in New York. It is high noon on the high seas. This session could be in lhe last.

The hottest issue is whether agreement can be reached on mining the apparently vast deposits of manganese, cobalt, nickel and copper in the deep seabed. Poor countries want mining controlled by an international authority run, in effect, on U.N. lines. Land-based producers of these minerals demand protection. Land-locked states want a distribution formula not favoring coastal states.

In the United States, internationalists see seabed mining chiefly as an instrument of diplomatic conciliation and international economic aid. Industry and strategy-minded interests note that the United States is the largest consumer and the technological leader and that it currently imports 98 per cent of its manganese and cobalt and 75 per cent of its nickel. These interests point to OPEC's example of price-gouging and political embargo and argue for substantial national and private access to seabed riches. The administration speaks softly in the language of diplomacy and waves discreetly the stick of unilateral mining legislation. If satisfactory agreement is not reached in New York, the United States will likely proceed on its own.

The ever more desperate quest for sure supplies of finite resources has created intense pressures on nations to take ever larger national bites out of international territory in the high seas. The United States endorsed the concept of the deep seabed as the "common heritage" of mankind in 1970 but the concept has never been realized in practice. Yet it is not trite sentiment that impels the international community to preserve as much of that concept as remains within its reach. Without agreement on this and other issues of the oceans, there will be discord. And who is to say that the resulting exacerbation of world economic and political tensions would not lead in the end to armed conflict?