Three hundred and sixty miles off St. Simons Island, Ga., the dawn broke gray and overcast, a sagging sky spitting rain at an ocean of four-foot swells.

The ships was steaming northward at 15 knots against a northwest wind, occasional seas spuming over the port bow. Temperatures had dropped into the 50s and winter was capturing the ship once again.

Cold is measured on a tanker not only by the crew but by the cargo, which must be kept warm enough not to boil away. Different oil grades require different temperatures. The Saint Petersburg carried two different grades, and both had been loaded in Aruba at 105 degrees and were expected at 90 degrees in New York.

At mid-morning, 3 1/2 days into the five-day voyage, pumpman Antonoio Torres, 39, ventured forward onto the windswept main deck, uncapped a small green hatch on each of the two port-side cargo tanks and hauled up thermometers suspended in the oil below. Both read 90 degrees.

Since near-zero temperatures were waiting for the ship farther north, he then turned a green wheel-like valve handle to send superheated steam into small pipes snaking through the cargo tanks and keept the cargo warm.

Oil, after all, is what makes tankers different from other ships.

It shapes their distinctive lines and structures, routes them from pipeline to pipeline instead of port to port, creates their peculiar shipboard hazards and makes every one a potential environmental disaster.

It also makes possible enormous profits for a tanker's owners and makes them very, very reluctant this season of sinking ships and oil spills to permit a closer look at tanker operations.

Exxon, whose tankers are described by the Coast Guard as generally well-kept ships and whose executives have been stung by recent general indictments of the tanker trade, agreed with unusual speed to a request to ride their ships. But Exxon executives in New York were very, very nervous.

The reason for their nervousness, in part, is the very nature of tankers, which without constant attention leave a trial of oil wherever they go.

Coast Guard spokesman say only about 15 per cent of the oil spilled in the area comes from major tanker disasters like the Argo Merchant wreck off Nantucker last month or the Torrey Canyon spill in 1969.

The other 85 per cent, they say, come from oil pumped over the side in bilg and tank cleaning operations, oil spilled in loading and unloading, and other shipboard procedures on tankers and other ships alike.

Ten years ago, tankers and other ships routinely pumped only bailast and bilge water into the sea to get rid of it, but modern cargo handling procedures permit tankers to pump ballast and waste water from tank cleaning operations into a slop tank where the oil and water areallowed to separate. The water is then pumped overboard, monitored by a machine which stops the discharge when the oil content of the water reaches 50 or 60 parts per million. The new cargo is then loaded on top of the remaining oily waste.

Likewise there are drip tanks under the loading and unloading pipes, procedures to prevent overflow, jammed valves, broken hoses and the like.

All of these however, require time, trouble and attention, and a major commitment from the owner in money and crew training.

It is good public relations, if nothing else, for a company to make that commitment, as Exxon obviously knows. A letter to captains governing use of oil dispersants after an oil spill states: "Your prompt action may avoid a heavy fire as well as avoid adverse publicity to Exxon."

A plague on the bridge of every Exxon ship declares it company policy that "the avoidance of pollution incidents is a matter of major concern and ranks second only to the safety of the ship and her crew."

There are videotape training films in several languages, and omnipresent, multilingual pinup clandars portraying tawny women beggin for clean seas.

It is difficult for a reporter riding a new ship on a short voyage to see how effective such efforts are, aside from noting an apparent general attitude among the Saint Petersburg's crew that pollution abatement procedures are a matter of course.

With luck, one occasionally encounters truly guideless people less concerned with possible bad publicity than with communicating the fascination and challenge of their work.

One such man is Oystein Dahle, 39, process manager of Exxon's Lago Refinery in Aruba, one of the largest refineries in the world.

Complimented on the oil-free appearance of therefinery's nearby waters, he replied: "We have procedures for much of it, but we are actually still leaking quite a bit of oil.

"The refinery, you see, has been here nearly 50 years and the coral beneath it has become saturated with oil. The oil actually seeps out of the coral into the water, despite everything we do. It's an absolutely fascinating problem."

Dahle pointed out an example of the seepage, described floating booms and walls built to contain it, and spoke with the enthusiasm of a man for whom pollution is truly, not a problem, but a challenge.

Another voice of candor was Henry O. Nicol, a burly engineer who superivses tanker repairs for Exxon in Aruba. Exxon officials had originally selected another, the 7-year-old Esso Karachi for the reporter to ride, but it was sidelined at the last minute for what two Exxon officials described as "minor structural cracks."

Nicol, descending into the oily gloom of the cargo holds, pointed out that the cracks, though hard to spot, weren't minor at all. They amounted to a 50-foot swath of deck that had flexed and corroded free of the Karachi's structural frame at a point in the 558-foot hull that takes the greatest strain in heavy seas.

"Something like this could continue all the way around the hull," he said. "In a heavy sea it could the ship apart."

If it hadn't been for a mate on the Karachi who spotted the loose decking and Nicol, who understood what it meant, the Karachi might have sailed again, unrepaired.

Nearly 10 per cent of the ships that put in at Aruba each year need similar repairs, Nicol said.

What of the tanker owners and crewmen who do less? Exxon's accountability is dictated in part by its corporate visibility: the same name that's on its tankers is one its gas pumps.

What of the owners permitted in anonymity by Liberian registry laws who put unsafe tankers in the seas? And what of the major oil companies that charter their ships, as Texaco chartered the Argo Merchant?

Exxon's Dick Lyon, operations coordinator of the company's tanker division, says Exxon supports greater inspection authority for the Coast Guard, stronger international laws, and an end to the provisions of law in flag of convenience countries that permit tankers owners to hide their names.

"We knw where the bad ships are," he said. Exxon, he said, screens any ship it charters extensively. "Four of the eight ships involved in recent accidents were offered to us for charter," he said. "We turned them down."

Lyon, however, says "legal problems" prevent Exxon from sharing with the public its knowledge of the unsafe ships with which the public may have to cotend.

North of Cape Hatteras, the Saint Petersburg ploughed through falling snow and a rolling gray sea that steamed eerily as if a mountain of dry ice were somewhere that steamed eerily as if a mountain of dry ice were somewhere below.

Below instead, among the 700 wrecks sunk in the legendary turturlence off the cape over the centuries, lie the broken hulks of 31 tanker torpedoed by Nazi U boats during the first six months of World War II. The tankers spilled their oil on the beaches of the Outer Banks where sandpipers flock today in an environment long since healed. Once supertanker of today carries more oil than all 31 of those ships.

At 10:45 p.m. Thursday the Saint Petersburg slowed off Ambrose Light to pick her New York pilot. He was Edmund J. Haggerty, 41, a rough but amiable 20-year-old veteran in a fur hat, who crackled orders over his walkie-talkie as he guided the ship up the channel toward the lights of the city.

"Jesus, Captain, you would have froze your tootsies if you'd been here last night," he said to Neri, who huddled in his captain's chair with the quiet pain of disposessed authority. 'Seven below! We had to anchor one tanker right heree,e 400 feet from another one."

"But we are 628 feet long," said Neri, gently.

"Well, there was nowhere else to put them. Some tankers don't have the proper facilities for heating the cargo so they take longer at the dockers unloading. We had one in here, his whole load froze up to a lump of tar. He's in great shape."

"Got enough room there, Ed?" said a voice from his walkie-talkie. "I'm pouring it on."

"Yeah, go on by Tom," said Haggerty.

An immense container ship boiled by, less than 30 yards to port, her cargo containers stacked on deck like the blocks of some Brobdingnagian child.

Above the ship the lights of the Verrazano Narrows Bridge glittered in the night like a string of jewels.

"Jesus, said Haggerty. "Prettiest night I ever saw."

At 1 a.m. Thursday the Saint Petersburg anchored off Staten Island. Haggerty had guided her into position with the aid of the ship's 850 horsepower bow thruster, a reversible propeller in a side-to-side tunnel through the ship's bow. "Just like having a tug up there," growled Haggerty with approval.

A late vacancy in the anchorage had given the ship plenty of room to swing in the tide. Within minutes an [LINE ILLEGIBLE] alongside to begin unloading her cargo. The voyage was over.