General Dynamics Corp., a major defense contractor, is proposing to build a fleet of submarine tankers to carry liquefied natural gas (LNG) beneath the Arctic ice.

The proposal, drafted by senior executives of the company's Electric Boat division, builder of the Navy's Trident nuclear submarines, was presented at a technical conference in Germany last week and is now circulating in Washington.

It calls for construction of massive tankers, each capable of carrying 91,100 cubic meters of gas per day, which would take on gas at a submerged Arctic terminal and ferry it out to an open-water port in eastern Canada or Europe. The proposal says the tankers, which would cost an estimated $700 million each if powered by methane gas and $725 million each if nuclear-powered, would be "competitive economically" with a fleet of ice-breaking surface tankers under study in Canada and cheaper than a pipeline.

"It's a feasibility study," said L. E. Holt, a representative of Electric Boat. "It asks if such a system is technically feasible. The answer is yes. It asks if it's economically viable. The answer is yes." The next step, he said, is to drum up interest among potential customers.

The idea of nuclear-powered underwater behemoths, 1,470 feet long and 228 feet wide, plying the shallow waters beneath the polar ice is not so novel nor bizarre as it appears, knowledgeable maritime sources said. It represents a refinement of a proposal that was seriously studied in the 1960s, before the construction of the Alaskan oil pipeline, to transport crude oil from Alaska's North Slope. The rise in energy costs since then could make a submarine tanker fleet an economically realistic proposal, maritime experts said.

The Electric Boat proposal was prepared by P. Takis Veliotis, the shipyard's general manager, and his deputy, Spencer Reitz. Veliotis, an experienced builder of surface LNG tankers, has for the past four years been director of the submarine con struction program at Electric Boat's Groton, Conn., shipyard. The first Trident missile submarine is to be delivered at the end of this month, after a long period of management snafus and multibillion-dollar cost overruns that brought Veliotis into open conflict with the Navy.

Transportation of liquefied natural gas is far more difficult technically than transportation of crude oil because it must be maintained at a temperature of minus 259 degrees fahrenheit. Surface LNG tankers are among the most expensive and complex ships in the civilian merchant fleet.

The Veliotis-Reitz proposal, however, says that the advantages would offset the costs, through the fleet's ability to "deliver a constant cargo volume at uniform, predictable scheduled intervals year-round, regardless of surface ice and weather conditions."

Their proposal calls for 14 nuclear or 17 steam-powered ships, loading terminals and repair facilities, at a total capital cost of $13.9 billion for a nuclear fleet or $16.2 billion for a steam-powered fleet--more costly because of the longer hulls required to surround the fuel tanks and the need for more total ships to haul the same amount of gas.