Diplomats here say that the commission set up under the Law of the Sea Treaty signed late last year has strengthened its credibility in its first decisions - and paved the way for deep seabed mining in the not too distant future.
During its first session in Jamaica, ending last week, the Preparatory Commission:
* Appointed as its chairman J. S. Warioba, minister of justice of Tanzania, widely considered here to be tough, pragmatic, serious, and intelligent. Representatives from developed and from developing nations hold him in high regard.
* Decided that all the important decisions to be taken by the commission - particularly with regard to rules and regulations concerning ocean mining - will be by consensus. Thus, it is said here, a ''tyrannic majority'' will not be in a position to impose its will on any one country or to crush the interests of a minority - presumably of industrial nations.
The Preparatory Commission will meet again in New York in August to start establishing precise rules and regulations for deep seabed mining. Reportedly, some industrial countries which have already signed the treaty, such as France and Japan, as well as others such as West Germany and Britain which are considering signing it, are eager to protect their interests (financial and technological) by having adequate rules and guidelines established by the commission.
The United States continues to reject the treaty. The Reagan administration opposes restrictions on free enterprise on a global scale and objects to multilateral solutions in general. Despite considerable diplomatic efforts, however, Washington has failed to stop France, Canada, and Japan from joining the Law of the Sea Treaty. And there is solid evidence that, even though West Germany and Great Britain do not want the US to be isolated, both governments may sign up before the year is over.
The Soviet Union has already announced that it intends to register as a pioneer investor in ocean mining. This means that it will receive the first exploration license. India and China are expected to follow suit.
So far, the industrial countries have not registered because they have not yet sorted out their differences and been able to determine which areas should be given to whom for deep seabed mining. US ocean mining companies belong to consortiums with European, Canadian, and Japanese firms.
The stakes are high. The potato-sized nodules to be mined contain nickel, copper, cobalt, and manganese. Since the Law of the Sea Treaty has now become part of international law, companies will find it difficult to mine the ocean floor on their own, without the authorization of the treaty's Seabed Authority. Banks are not expected to finance such attempts for fear of litigation and of being ultimately branded as law-breakers by the International Court in the Hague.