Sea Law talks break through nine-year squall

A civilized deed in a sometimes seemingly irrational world. An affirmation that cooperation across borders and ideologies can take precedence over narrow self-interest.

This is how diplomats here describe the comprehensive Law of the Sea Treaty expected to be adopted Friday by the Law of the Sea Conference at the United Nations.

In the words of the conference's chairman, Tommy T. B. Koh of Singapore, ''This treaty represents the single most important international diplomatic event since the creation of the United Nations.'' Delegates from many geographic regions and many ideological viewpoints agree with this assessment.

Negotiations toward this treaty lasted almost nine years. They involved 157 countries and were on the brink of collapse more than once. One year ago the Reagan administration walked out on the conference a day before it was scheduled to resume. Until last December it looked like the United States would not further negotiate with other countries on the issue.

In the end pressure exerted by its allies (Japan, France, Britain, and West Germany) on the US was decisive in getting the US not to play the role of the odd man out or to boycott the treaty, according to informed sources. Many old Law of the Sea hands believe that the Reagan administration will not itself sign the treaty in December, but that the next US administration ''will come on board ,'' to quote one Western ambassador.

The treaty settles the question of who owns the oceans. It affects all aspects of maritime life: commercial, economic, legal, military. For instance, it gives the ships of the world the right to pass through important straits and waterways. It allows each country an economic zone of 200 miles, a territorial zone of 12 miles. It settles the questions regarding fishing rights and continental shelves.

In particular, it determines the rules and procedures of deep seabed mining (of mineral-rich potato-sized nodules containing cobalt, manganese, nickel, or copper).

An enterprise representing all parties to the treaty will own the riches of the ocean floor and parcel them out to private as well as to state-owned concerns. Limits to deep seabed mining have been set so as to protect land-based mining countries such as Zaire, Zambia, Canada, and Chile. Procedures for the transfer of seabed mining technology by private enterprises of industrial countries to the enterprise have been determined, so that all nations will get a fair share of ''humanity's common heritage.''

Many countries, including the US, had to settle for less. Gaps between positions taken by numerous delegations on a great variety of problems were deep and cut through ideological, economical, and geographical lines. In some instances the Soviet Union and the US stood shoulder to shoulder, whereas Canada sided with the developing nations, for example.

The US objected to many aspects of the treaty because it does not fit with the US heritage of free enterprise. It obliges private concerns to transfer their know-how to a limited kind of world government.

Bargaining was difficult. It took Mr. Koh's patience and gift of gentle persuasion to get suspicious industrial countries and angry African countries to lower their demands.

The sometimes bluff tactics and resort to ultimatums of US delegate Leigh S. Ratiner proved no match for the subtler approach of others like Alvaro de Soto of Peru, who chaired the group of ''77'' (developing nations).

The US and other industrial nations still managed to extract substantial concessions from the ''77.'' For example, the ''grandfather clause'' gives ocean mining companies the right to explore seabed minerals in international waters before ratification of the treaty. When the treaty is ratified, the companies will get the same site for exploration.

The clause under which they will be required to transfer their technology has been somewhat softened and made less compelling. Also the revision of the treaty in 20 years will have to be made by consensus, meaning that the US will be able to resist changes it opposes and will not simply be outvoted.

Even so the US has until December to decide whether to actually sign the treaty. It is scheduled to be formally signed in Caracas, Venezuela, next December at a final and ceremonial convening of the conference.

Certainly Japan, and probably France and Germany, will sign the treaty, according to reliable sources. Even if it were not signed by the US, the treaty would become customary law. ''It will have a dynamic of its own, and in the long run the US could not afford to remain aloof from it inasmuch as it represents the whole world's legal opinion,'' a Western legal authority says.