Since 1964, several international consortia including such major U.S. corporations as Kennecott, U.S. Steel, Lockheed and Sedco have been prospecting under the Pacific about 800 miles south of Hawaii, looking for manganese and other valuable minerals.

Tens if not hundreds of millions of dollars have been invested, and it is believed that any group wanting to start commercial mining of the ocean floor would need at least $1 billion. Estimates put them three years away from even testing the collection of manganese nodules.

No one country claims that area of the Pacific Ocean, so the exploratory operations have been carried out under the internationally recognized doctrine of reasonable use of the high seas.

Enter the age of environmentalism. Now laws have been passed and rules are in the works. Even the international groups that have been at work all these years face the prospect of U.S. regulation.

At first glance, it looks like another example of the federal government pushing its regulatory powers to the limit, making rules to cover all deep-sea mining operations in the Pacific area or anywhere else in the world to prevent American-involved corporations from causing environmental damage to the ocean floor.

But it is more complicated than that. The law Congress passed last June to prohibit U.S. citizens from exploring for mineral resources in the ocean floor without a federal license was originally promoted both by the government and by the corporations already involved in the work.

The law was designed to protect the activities of the pioneer prospectors. While the National Oceanic and Atmospheric Administration (NOAA), which was given responsibility for developing rules to protect the ocean floor, is struggling with that problem, no U.S. citizen is permitted to start any new seabed exploration -- except, of course, for the ones who are already there. They were given an exemption until the licensing rules are made final.

The already-exploring companies wanted the law, which established rules under which they could work and which they could take to banks from which they had to borrow money. With it, they could prove that nothing unexpected would emerge from the government in Washington somewhere down the road to hurt their investments. The companies also were fearful that somehow Third World countries or the United Nations might get into the picture. For the past eight years, an international Law of the Sea Conference has been wresting with just such problems.

The U.S. government wanted to make certain that the environment of the ocean floor, despite its international character, was not harmed -- at least not by U.S. citizens. And some officials hoped a U.S. licensing procedure for under-ocean activities might push the Law of the Sea group into agreement, perhaps along the same lines as the American statute.

NOAA now wants to identify the companies that have been at work and thus qualify for exemption, according to interim regulations that were carried in the Nov. 20 Federal Register (page 76661). But the regulations go further than that -- a fact not lost on the companies involved.

NOAA also wants a description of exploration activities carried on before June 28, 1980, when the law was enacted, an estimate of expenditures up to that time, a statement of whether a license application will be filed when required and whether exploration will continue until that date. The companies won't have to include locations of past or future exploration or "prospective mine sites."

In addition, NOAA wants details of future exploration voyages by the exempted companies, including dates, types of activities and "an estimate of the anticipated extent of seabed disturbance and effluent discharge." A post-voyage report is also required within 30 days of the end of such a trip.

The hooker for the exempted companies may be in a section of the interim regulations that gives the administrator of NOAA the right to suspend the exploration activities of a company when "necessary to prevent a significant adverse effect on the environment."

A NOAA official said recently that no such suspension is foreseen if the companies use such nondisturbing equipment as underwater television; "side scan sonar," which sends out sound pulses; grab samplers and core samplers, which barely disturb the seabed. s

But when they move to mining collectors and lift systems, the official suggested, NOAA may have to step in.

The deep seabed exploration and mining license regulations are not expected to take effect until next Sept. 1, and application reviews may not be completed for 15 additional months, so the exempted companies probably will be exploring under these vague, interim regulations for two years or more.