It is a treasure hunter's dream, a prize so magnificent as to enflame even the richest of emperors. Envision a vast plain, hundreds of miles broad, covered with some of the scarcest and most sought-after minerals in the world. The minerals are worth billions and billions of dollars and are just waiting to be picked up. In centuries past, such prizes have set nation against nation and outlaw privateers against all.

This time the riches come in "nodules," charcoal-black potato-sized lumps small enough to pick up by hand. The origin of the nodules is something of a mystery. Their content is not. They are loaded with copper, manganese, cobalt and nickel. But there is a catch: the mineral-cobbled plain is on the bottom of the world's oceans, three miles below the waves. Recovering these minerals will be awkward and expensive. In the words of one treasure-seeker, mining the nodules will be "like standing on top of the Empire State Building on a windy night and trying to suck peas off the sidewalk with a straw."

Only the rich can set off on a rush off this. A company named Deepsea Ventures in Gloucester Point, Va., has already claimed a piece of the Pacific Ocean the size of South Carolina. Deepsea Ventures is owned by a consortium made up of some industrial goliaths: United States Steel, Sun Co., the Belgian steel firm Union Miniere, the Italian oil company Samim, and, in the background, Tenneco. Four other consortia have also formed to go after the minerals; they include such multinational conglomerates as Lockheed Missiles and Space, Kennecott Copper, Mitsubishi Industries, British Petroleum, and Royal Dutch Shell. They are ready to carve up the ocean floor the way Western nations once divided continents.

Unfortunately for these hightech pioneers, their frontier has turned out not to be as wide-open as first thought. Like the Antarctic continent and the dark side of the moon, the bottom of the sea seemed technically to belong to no one in paticular. But some nations have claimed it belongs to everyone equally. Developing nations, watching the industrial world gear up for an era of what they call "submarine colonialism," contend that the nodules lie on a global commons, where the old rule of "first come, first served" does not apply. They argue that the nodules should be mined cooperatively and any profits shared. It is an argument that cuts to the heart of today's debate between rich and poor nations, and it so fires up the Reagan administration that it may topple a 15-year effort to make way for ocean mining with a delicately balanced Law of the Sea treaty.

The future of the deep sea mineral rush may depend on what the United States does when treaty negotiations resume this week in Geneva. In the past, the United States has supported a compromise, first proposed in 1976 by then-Secretary of State Henry Kissinger, that would let private corporations go to work on the sea bed alongside a public mining company under the eye of a new International Seabed Authority. The public profit-sharing company would receive seed money from the industrial countries and have the right to buy their new mining technology.

But the Reagan administration is unhappy with that compromise. Officials fear the Seabed Authority's power could be used to deny U.S.-based companies access to the nodules, which offer this nation a new source of manganese and cobalt, two strategic minerals critical for hardening steel. Both manganese and cobalt currently must be imported from politically Both manganese and cobalt currently must be imported from politically parcarious countries such as South Africa and Zaire.

"We are importing from foreign nations the most critical elements of our civilization," Secretary of the Interior James Watt has said, "the universal building blocks of an industrial economy."

Beyond the strategic consideration there is a matter of ideology. "We may be committing ourselves to certain things that cut against the free-market orientation of the Reagan administration," says Assistant Secretary of State James L. Malone, who will head the new negotiating team. The old bipartisan delegation, branded "internationalists" by conservatives, was dismissed suddenly in March on the eve of what was to be the final negotiating session.

In Geneva, the United States will want more assurance that companies like Deepsea Ventures can help themselves to the manganese nodules of the South Pacific. But chances are the developing nations won't agree to major changes in the current text, says former U.S. negotiator Elliot Richardson.

If a better deal for private enterprise can't be struck, the United States has the option of withdrawing from the negotiatings, administration officials say. It would be a risky course. "If the United States assumes an attitude of confrontation and says we just reject everything in block, it would arouse a tremendous amount of resentment. It wouldn't stop the other states from adopting the present text," says Arvid Pardo, who as a diplomat from Malta helped launch the negotiations in 1966. "One has to realize the United States isn't what it was 20 years ago. It can't take on everybody."

A more likely outcome of U.S. withdrawal would be total collapse of the treaty convention, and that would probably discourage investors. Most mining companies halted development of their new billion-dollar mining systems a year ago, afraid to go ahead without an international guarantee for ocean claims. For seekers of this distant treasure, the greatest challenge of all may be political.

Deepsea Ventures, for one, says it may mine the ocean floor even without a treaty. "We would hope the United States would protect us," says Jeffrey Amsbaugh, president of Deepsea, "just as if we were fishing out there."

Indeed, if the Reagan policy shift leads to collapse of the treaty negotiations, the result might simply be a return to the age when might made right on the high seas. The Defense Department, a long-time backer of the treaty because it would assure the Navy free passage through straits and boundary waters, now qualifies its support by saying the navigation provisions must be balanced against the need for strategic materials. Military needs have changed since the treaty talks began, the thinking goes, and in the Third World today morale is low and the disarray great. The United States had already begun to negotiate one-on-one reciprocal agreements with other industrial powers in which each country agrees to respect the other's mining claims at sea. These agreements are intended to promote ocean mining until a treaty is adopted, but Deepsea Ventures hopes it can form a permanent basis for investment. "The countries I'm most interested in agreeing with are the ones who will be doing the mining," Amsbaugh says. Collapse of the treaty, one British diplomat has predicted, would set off "the biggest smash and grab since the European powers at the Berlin Conference carved up black Africa."

For more than 20 years, the concept of a Law of the Sea treaty had no bigger defender in the world than the United States. The world's major maritime powers have been trying to settle peacefully the dispute over who owns the oceans ever since man found out the world was round and Pope Alexander VI, in 1494, drew a line west of the Cape Verde Islands to divide between Spain and Portugal all the known world and its waters. This first delineation proved imperfect -- the Dutch and the English in particular found fault with it -- and the ocean was swiftly crisscrossed with counter-claims. Under the circumstances no merchant ship was safe at sea unless accompanied by a man-of-war. Ultimately the rising cost of insurance, not international altruism, promoted adoption of the principle of freedom of the high seas. By 1750, nations were withdrawing their territorial claims to a limit they could reasonably defend: the range of a cannon, three miles offshore.

Jurisdictions began to creep seaward again after oil companies waded into the offshore shallows in the 1920s. The United Nations tried to halt the advance of offshore claims with its first Law of the Sea treaty, a half-hearted agreement of which the chief fault was that it had not looked very far into the future. The treaty was signed in 1958, only a matter of months after John Mero, a 27-year-old graduate student at the University of California at Berkeley, published a paper on manganese nodules and opened the way to a vast ocean resource conflict that the signatories had not foreseen.

Manganese nodules were dredged up from the ocean floor for the first time in 1872 by a British oceanographers, but for years the only interest in them had come from scientists curious about their origin. Some thought the porous stones might be meteorites that had splashed into the ocean. Many scientists figured they had been scattered by the explosion of undersea volcanoes. As it turned out, neither guess was correct.

They grew there.

Alchemists have long attempted to draw minerals such as gold and salt directly out of sea itself, but nature has had its own method all along.

The ocean is really a broth of dissolved minerals. In the past few years, geophysicists have traced some of those minerals to underwater geysers erupting along seams torn in the ocean floor by the spreading of continental plates. When the heated water from beneath the earth's crust trickles upward, the shock of meeting near-freezing temperatures sometimes causes the minerals to drop out of solution and form slow-growing stalagmites of zinc, copper and iron. If the geysers shoot out quickly they are known as "smokers" -- in a floodlight they appear black with minerals, which disperse and are joined by others robbed from the continents by rain.

Where bottom currents are slow and the fallout of silt from river systems not too heavy, these dissolved minerals eventually precipitate around some nucleus lying on the ocean floor -- a bit of clay or, occasionally, a shark tooth or porpoise earbone (both made of material called apatite, which lasts longer than the rest of an animal's remains). No one is certain why this precipitation takes place, though scientists suspect that there is an electrical attraction between the growing nodule and the dissolved minerals, which are drifting in the form of electrical ions. In the perpetual midnight of the ocean floor, the nodules have been growing like rock candy. A cross section of a nodule shows growth rings like an onion's. A nodule three inches across may be 3 million years old.

In 1957, oceanographers on an International Geophysical Year expedition east of Tahiti pulled up a load of nodules containing unusually high concentrations of nickel, cobalt and copper. Comparing the new assay results to older specimens that had been heavier in manganese and iron, Mero wrote a research paper discussing that nodules' potential as a mineral ore. That paper, and a book by Mero that followed in 1965, provided the impetus for an investment of about $400 million in ocean mining to date.

"Except for the Law of the Sea I think we would have been mining the nodules a long time ago," Mero says today. "Now that the lawyers have moved in, I have my doubts about it ever happening."

Mero's manganese nodule is a modest little lump of next to nothing. Because of the way it grows, this ore is about one-third air when pulled to the surface, giving it a heft only slightly heavier than pumice. By weight, dry, it is 15 percent iron, but since iron ore in Minnesota is more like 50 percent iron, nobody would waste money trying to extract iron from nodules. Indeed, traces of 74 minerals have been found in the nodules, but, as in any ore, most of them are considered waste.

Even the valuable minerals in a nodule appear in small traces. A ton of nodules would produce only 30 pounds of nickel, used to make stainless steel alloys and refine gasoline, and only five pounds of cobalt, used to harden the high-grade steel used in jet engines. It would take 182 tons of nodules to produce enough cobalt to build one turbofan engine for an F-16 fighter plane. But that's the way it is with these minerals; no richer veins are to be found on land.

Although a four-ounce nodule the size of a hen's egg contains about two cents worth of minerals, as Mero observed in his 1957 paper, the things do add up. Recently the U.S. Bureau of Mines assayed a ton of nodules from the South Pacific -- not even enough nodules to fill up a canoe. This ton of nodules contained $109 worth of nickel, $72 of cobalt, $25 of copper, and $42 of manganese. It also contained $41 worth of molybdenum. By contrast, a ton of copper ore from an Arizona open pit mine is likely to have a value of $8.50.

'I guess you would say John Mero was the guy who initiated ocean-bottom mining," says Raymond Kaufman, the vice president of Deepsea Ventures. "In every new industry there's a time for somebody like Mero, and his phase was in the beginning. He kind of fell out of it after a while. Now we're into the commercial development phase."

Kaufman and others in the industry claim the difficulties of ocean mining have been underestimated by politicians who like to exaggerate the profits to be raked up from the ocean floor. It will take as much as 10 years of production, at 3 million tons of nodules a year, before a company can make a return on the $1 billion or more that it will cost to mount a single mining operation, according to the companies. "These projects are considered right on the verge of marginal," Kaufman says.

In June 1978, technicians from Deepsea Ventures took a converted ore carrier to their Pacific claim in the heart of the richest region yet discovered, a 3.000-mile-long carpet of nodules between Panama and Hawaii, to try out a suction system first tested on land in a flooded mine shaft. A sled the size of a pickup truck, carrying their experimental "dredgehead" miner, was dropped into the sea. For nine days the technicians lowered the mining machine, pipe section by pipe section, until at 15,000 feet it settled on the bottom. The pipe was filled with water, and then air pumped from above was injected into the pipe several thousand feet below the surface. The light-density air-and-water mixture in the top of the pipe was forced upward by water pressure on the bottom, creating a continuous suction through the eight-foot-wide vacuum mouth of the dredgehead.

The mining machine cut a swath through the nodules, riding its sled runners along the bottom goo as the ship trolled from above at a speed of one knot. Even with careful navigation on the surface, such a system is not very efficient. Kaufman says his group will be happy if the first-generation commercial-scale miner can bring up half the nodules in a given area.

Other companies interested in collecing the nodules consider Deepsea Ventures' approach rather prosaic. "Basically it's the industrial approach against the aerospace," says Marne Dubs, director of Kennecott Copper's ocean resources division. A much more sophisticated -- and riskier -- mining system is being developed by the consortium led by Lockheed.

Lockheed plans to use a mining device that crawls along the ocean floor under its own power, inhaling nodules for a 45-minute journey to the ship, where technicians will be directing its movement by remote control. Because the ooze on the bottom is too soft for any tracked vehicle, Lockheed's miner moves by means of a pair of archimedean screws the size of Polaris missiles. For added precision during its deep-sea test, Lockheed leased the former spy ship Glomar Explorer, whose ability to hold its position with computer-controlled side thrusters and to "crab" sideways into high seas proved as helpful fishing for manganese nodules as it was fishing for a sunken Soviet submarine under contract to the Central Intelligence Agency in 1974 (when its cover was that it was exploring for nodules for Howard Hughes).

Guiding such a rig by underwear television cameras, Lockheed believes, will allow miners to "lawnmow" the nodules and leave few behind. Lockheed's gamble is that its sophisticated miner won't break down while on the ocean floor and need to be cranked back up to the surface, pipe section by pipe section, for repairs -- a round trip that could shut down production for a week.

Commercial-scale systems are still eight to 10 years away from production. Everything in them will be of behemoth proportions. Three miles of pipe will weigh more than a tugboat. The mining ship will be as big as a supertanker. Lockheed expects to use a dredgehead with a 120-foot-long screws and a vacuum maw as wide as Pennsylvania Avenue.

The growing interest in ocean mining, together with the continued march to sea by coastal nations, puts pressure on the United States to come up with a new Law of the Sea treaty.

The Reagan administration has not yet proposed an alternative to the international mining regime in the current treaty text; its strategy will depend on how the developing countries respond this week in Geneva. It is clear that any new compromise would have to satisfy the private corporations whose concerns the administration shares.

The more the mining companies saw of the proposed Seabed Authority, the less they liked it. They objected to a provision that would force them to sell their mining equipment to their comeptitors. The most outrageous of the treaty's design-by-committee problems, they complained, was a requirement that the agency discontinue mining of nodules if necessary to keep mineral prices high and protect major exporters of nickel and cobalt (a provision pushed through by, of all allies, Canada, the world's biggest producer of nickel). "That's the real poison in the treaty," says Kennecott's Dubs. The miners were suspicious of the Seabed Authorityhs power to grant mining claims, and feared its discretion could be used for vindictive political purposes. Defenders of the treaty said the fine print would protect against such an abuse. "They want assurances they can't even get in their own country," says James Barnes, director of the Center for Law and Social Policy, a Washington public interest law firm that monitors "world equity" disputes.

Administration spokesmen themselves stress a second reason for objecting to the treaty: America's need for certain key minerals, and a corollary concern about the potential for Soviet bloc domination of the Seabed Authority.

The government has listed 80 strategic minerals and metals of which the United States would fall short during a war lasting three years. This doesn't really mean North America is bare of those key minerals. For example, there are low-grade manganese deposits in Maine and Minnesota. But the world price would have to be five times higher to make manganese produced from those states competitive with foreign sources.

It's the same with cobalt. Traces of cobalt are found in the American West, but the last time they were mined was when the federal government subsidized production at Blackbird, Idaho, during the Korean War. Even when the world price tripled after rebels in Zaire disrupted mining in 1978, no one moved toward the American cobalt deposits. In June, the United States paid $75 million to Zaire for 5.4 million pounds of cobalt, the first time strategic materials have been added to the nation's stockpiles in two decades.

This feeling of vulnerability has prompted Secretary of the Interior Watt to push for more mineral prospecting in wilderness areas and reconsideration of the American position in the Law of the Sea negotiations.

But ocean bed mining is too far to solve the Reagan administration's immediate problem of shortages. "We can't lick 'em next year with stuff pulled out of the ocean 10 years from now," says John Morgan, chief staff officer for the Bureau of Mines.

There is a third concern expressed by oponents of the current treaty text, and it has less to do with the new fdsrontier of ocean mining than with fear of what lies beyond. In 1970 the United Nations unanimously declared the mineral wealth of the ocean to be "the common heritage of mankind." But this heritage belong to anyone who gets there first, or is it common property, making a company such as Deepsea Ventures nothing more than a poacher? As a symbol of the new resources awaiting mankind's ingenuity, the manganese nodules have been caught up in a conflict between ideological principles that may leave them down int he dark for many years to come.

"There would be recedent established here that would have an impact on a lot of other things in the North-South debate," says Assistant Secretary of State Malone.

A treaty proclaiming the resources of the moon and all other celestial bodies to be "the common heritage of mankind" is open for signature, though the Carter administration, whic;h initially supported it, drew back from ratification under pressure from many of the same companies that object to the current text of the Law of the Sea. A long-standing mini-treaty dividing Antarctica among 14 nations is now under siege by snubbed countries who believe the South Pole should be part of the global commons. Colombia, stirring up other countries, has tilted old ocean arguments 90 degrees and claimed "air space" extending 22,000 miles, giving it control of portions of the geostationary orbit over the equator used by communications satellites. How the Law of the Sea negotiations define "common heritage" will have an important impact on these questions and other current talks on allocating radio frequencies, orbit placements and even "technology" itself.

While few in the Reagan administration would advocate a return to shipping in the company of men-of-war, the question has now become, how far will the United States go in allowing a new international economic order, one based on public financing nad centralized planning and shared income, to supplant entrepreneurial captialism on its grand modern scale? Ronald Reagan's stated preference for the private sector over the public sector may play well in Peoria -- and in the U.S. Senate, which would have to ratify the new Law of the Sea -- but how will it play this week in Geneva?

"If you push mot of the mining companies they will tell you they'd preer an improved treaty," Elliot Richardosn says. "They don't want the government to push it across the delicate line."

Richardson cautions that the United States may be missing an opportunity. "The real threat to the treatynow comes from domestic conservative ideologues who fear creating a powerful new international body," he says. "The iro;ny is that a strong argument an be made that this is rally a useful precedent, given the evolution of multilateral institutions, in that it establishes that multinational corporations have an interest in the global commons."

"The treaty ought to be more tolerable to the have-countries because all it's taking away are expectations," says Richard J. Barnet, author of several books on global resource problems. "The symbolism of sharing power in this case is very important because it shares responsibility as well. It puts the Third World in a position o bieng not merely bargaining partners but actually taking some responsibility for production. Waht the United States most needs is a world order, and the one we have now is eroding very rapidly. The arguments against the treaty are premised on the assumption that we can continue with the present order indefinitely. If you believe that, then sure, the national interest is in promoting a free-for-all at sea."

A few of the real pioneers of ocean mining now fear it will prove politically impossible to budge the manganese nodules from the ocean floor. Arvid Pardo of Malta, whose eloquence first swept the United Nations into declaring the nodules to be "the common heritage of mankind," now dismisses the compromise public mining company as "stupid" and admits that his dream has been tarnished by the lengthy negotiations. "I had hoped for too much," he says.

But the former diplomat, who has ducked out of the ideological crossfire and is now a professor of political science at the University of Southern California, says he has not given up on his vision of the ocean floor as a cradle of unity. "It in effect it is possible to go ahead with international manatgement of resources, even in a small way, adn it is demonstrated to be resonable and profitable and efficient, we will ahve made a major conceptual step for mankind. If, on the other hand, and this is my fear, the whole setup becomes so cumbersome, so brueaucratic, so badly managed that it requires endless government subsidy, it will negate the concept of international management for many years to come."

The man whose book started the ocean mining industry burned himself out trying to launch a mining consortium of his own. But he made a good deal selling the rights to an underwater deposit of phosphates he'd come across in French Polynesia, and when it was time to get out of the rat race he was able to buy a ranch in northern California, where he lives today, growing grapes and writing another book, this one about the law of negativity that governs our social institutions.

There will be a chapter aobut deep sea mining and the Law of the Sea. "Mero's Law," says John Mero, "is that creating a bureaucracy always leads to the opposite of its intended goal."