'Operation Deep Sweep' sails off to search beneath the sea

Real voyages of discovery are hard to find these days. But 50 scientists embarking this week on a 200-foot research vessel believe they are taking part in such an adventure.

They are bound for Alaska on the first leg of a scientific odyssey: a year-long effort to study the geology of the floor of the Pacific Ocean. The quest will take the United States Geological Survey (USGS) ship Samuel P. Lee on a 40,000-mile, $12 million voyage stretching from the Arctic to the Antarctic.

''I know it's a bit presumptuous, but to me this trip is like the Lewis and Clark Expedition, in that we will be going into an area with unknown geology,'' explains David G. Howell, chief of the Pacific Marine Geology Branch of USGS, the wind blowing his dark, curly hair as the Lee steams out from San Francisco Bay. It is the most ambitious voyage in the agency's history, he explains: It will last longer, involve more people, and cover more territory than any previous USGS research effort.

Although billed as basic geological research, the voyage will emphasize gathering information to aid the discovery of undersea mineral resources and petroleum reserves.

Operation Deep Sweep - as the researchers have named the project - will be using a battery of scientific instruments to chart the mountains and valleys, faults and undersea volcanoes, which they encounter. On the trip up San Francisco Bay, the scientists demonstrated a number of these tools.

Most tools utilize seismic techniques. The ship beams sound waves of various pitches to the sea bottom and records the reflections. This allows the ship's computers to draw a picture of the geological strata up to 12 kilometers beneath the sea floor.

As the ship is working, it emits a range of sounds from chirps to booms. The reverberations of these varied sounds are picked up by detectors strung in two miles of plastic tubing trailing behind the ship or by refurbished military sonar detectors. The latter are three-foot-long canisters launched from the ship. After parachuting into the water, they bob to the surface and begin transmitting what they ''hear'' to the vessel.

This seismic information is fed into the ship's computers and stored on magnetic tape. In fact, while the ship is ''shooting'' a seismic line almost everything is controlled automatically. ''The big problem is boredom,'' admits Terry Kelley, who is in charge of the ship's instrumentation.

Partly for this reason, scientists will rotate on two- to five-week shifts throughout the voyage. The ship's crew will work three months on, one month off.

In addition, the Lee carries cameras that can take pictures when lowered as much as 10,000 feet below the surface. On their way north, scientists intend to use these to get some pictures of thermal vents that lie off the Oregon coast. These are undersea oases of warm water where unusual marine life has been discovered.

A deep-sea dredge that can pick up samples of the ocean floor from a depth of 6,000 to 8,000 feet, and a chemical laboratory for analyzing them, complete the Lee's tools of exploration. In the area of Samoa, the ship will combine forces with a West German research vessel to dredge up samples of cobalt-rich encrustations found on the top of undersea mountains. Cobalt is a strategic metal needed for making steel. It's a material which the US and West Germany depend on foreign sources to supply.

Unlike Christopher Columbus, the Lee's captain, Alan J. McClenaghan, will have difficulty getting lost. Electronic navigation gear will continually pinpoint the ship's position to within 50 meters. This precision is extremely important to the scientists trying to draw an accurate picture of the undersea geology.

Most of the Deep Sweep researchers' efforts will be aimed at what geologists call framework studies, studies designed to work out the broad outlines of an area's geologic structure. This allows geologists to pinpoint general areas that may have mineral or petroleum potential and rule out those that do not.

But even this basic research may prove controversial in the vicinity of the Antarctic. Currently, the United States is among the signatories of the politically fragile Antarctic Treaty. The pact prohibits commercial exploitation of the continent's resources and reserves it for scientific study. In 1973 the deep-sea drilling vessel Glomar Challenger stirred up a hornet's nest of concern when it struck natural gas in Antarctic waters.

Although Dr. Howell maintains that the type of work the ship is doing will not lead to the discovery of oil or gas fields, he admits that with certain types of highly sophisticated computer processing, the Lee's seismic measurements could bring out what geologists call ''bright spots,'' which are highly associated with such fields.

In fact, the prospect of ultimate exploitation of any Antarctic oil and gas was part of the reason the Circum-Pacific Council for Energy and Mineral Resources offered to raise $1.5 million from private sources to underwrite the Antarctic leg of the voyage. The council was founded by Michel T. Halbouty, an independent Houston oil man and a member of President Reagan's kitchen cabinet. It is made up of industry, government, and academic geologists from most of the Pacific Rim countries, including the Soviet Union, China, Japan, Australia, Canada, and the US.

''Industry should be interested in the Antarctic leg because of the potential oil and gas there. At present, the treaty prohibits commercial activities. Still , information like that obtained by the Lee will be helpful to companies in their long-range planning. And eventually a new treaty may be negotiated,'' Mr. Halbouty explains.

Antarctica holds an entirely different appeal for Dr. Howell, however. He is one of the proponents of a new theory of how continents grow and break up. This is called collage tectonics, because it holds that continents are built from a collage of fragments of crust that originate in other areas of the world. And Antarctica, considered the core of the ancient supercontinent, Gondwanaland, may further confirm this theory.

Working out the details of this theory, now generally accepted in geological circles, has major implications for the search for mineral resources, confirms Brent Dalrymple, assistant chief geologist of the USGS.

''Before plate tectonics, we were taught that the ocean was a mineral treasure-house, if only we could get to it. Now we know that there are not nearly the resources there we once thought. Collage tectonics is having a similar effect, only at a more detailed level.''

''Without research, we won't know how to find the resources, let alone how to exploit them,'' Halbouty says.