Only the waves slapping the shore of the Cheasapeake Bay broke the autumn stillness early that October morning as Henry Lee Cooper walked his rounds, checking the gauges that monitor safety conditions at the sprawling CovePoint liquefied natural gas terminal here.

Cooper was headed for the compressor shack when he saw it -- a frosty, transparent liquid bubbling from an electrical pump. He got on the walkie-talkie and called his boss, Charley Bromley, who came running.

Bromley immediately realized that the substance oozing onto the ground was extremely volatile liquefied natural gas.It was essential, he said, to cut off electrical power to the pump, because the slightest spark could trigger an explosion. The two men ran to the electrical substation where Bromley alerted the control room operator to the problem and cut off the power.

"And then," Cooper recalled, "it belew."

The Oct. 6 explosion, which killed Bromley, 31, and left the 30-year-old Cooper badly burned, touched off investigations by a half-dozen state and federal agencies. It also brought renewed warnings from critics who say it is courting a potential doomsday disaster to construct a liquefied natural gas terminal within three miles of a nuclear power plant. That is the distance from Cove Point to Baltimore Gas and Electric Co.'s Calvert Cliffs facility.

In the three weeks since the accident, preliminary ivestigations have found that the Cove Point plant was being operated entirely in accordance with existing regulations, that the explosion was caused by a design defect in a pump, and that the nuclear plant was in no way endangered by the incident.

But it is that very kind of no-fault conclusion that troubles critics of liquefied natural gas, among them Rep. Edward J. Markey (D-Mass.), the sponsor of House-passed legislation that would tighten controls on the shipment and importation of the super-cooled substance that can, when exposed to air, become extremely explosive.

Markey's interest stems from the presence of LNG plant in the heavily populated Boston suburb of Everett, which is in his congressional district. The nation's only other importing terminal for liquefied natural gas is in Savannah, Ga., harbor, although new ones are planned in California and louisiana. However, there are 125 smaller LNG storage facilities scattered across the country. The technology to liquefy gas was invented early in the century, out its use virtually disappeared for two decades after an accident in Cleveland in 1944 killed 128 persons.

Just a few days before the Cove Point explosion, Markey, in a letter to the Boston Herald-American, said an accident at a liquefied natural gas plant "might lead to a catastrophe on a par with the worst nuclear power plant accident, producing a fire storm destroying everything in its path."

After the Cove Point accident, the congressman came here and called for an investigation, warning that "in our haste to build energy facilities," the country may some day be faced with "a natural gas Three-Mile Island." The House Commerce Subcommittee on Power and Energy, of which Markey is a member, will begin hearings on Cove Point on Friday.

Earlier hearings in Washington have revealed that LNG, which is heavier than air, vaporizes and expands as it warms, eventually reaching 600 times its liquid volume, and moves with the prevailing winds. A drifting gas cloud could be ignited by a spark as small as one caused by an auto horn.

But investigators agree that the Cove Point blast did not threaten its nuclear neighbor at Calvert Cliffs. There is a hotline between the two plants, but according to John Metzger, media relations representative of BG&E. The special telephone is to be used "only if the incident were of such a nature as to affect the operation of the other plant," Metzger said, and "this isolated incident" did not meet the requirements of notification.

Maryland fire marshal James C. Robertson, who also investigated the explosion, agrees with Markey that existing regulations are inadequate. In a letter to the National Fire Protection Association, Robertson urged a change in national fire and electrical codes to establish specific standards for handling cyrogenic (very low temperature) materials. The code now says only that materials be "appropriate for condition and use." (Natural gas is transformed to liquid by lowering its temperature to minus 260 degrees Fahrenheit.)

Robertson said "there probably isn't a seal manufactured" to withstand such low temperatures as found at LNG plants. The fire marshal believes the seal that failed at Cove Point was manufactured to contain materials no colder than minus 70 degrees, and that it deteriorated, along with its sealing compound, from constant contact with the substance.

The seal in question, made of a hard-rubber-like material, is a product of the J. C. Carter Co., of Costa Mesa, Calif., a subsidiary of ITT. A spokesman for ITT said the company would have "no comment until the investigation is completed."

Another report, by the Coast Guard, reached a similar conclusion. In an Oct. 23 letter to John Van Dyke, general manager of the Cove Point terminal, Capt. J. W. Kime, chief of the port of Baltimore, said that while no violations were discovered, "in view of the explosion and fire ashore, the existing design is considered inadequate.

Kime issued an order prohibiting LNG ships from unloading at Cove Point until the defect is corrected.

Barring ships from the terminal cuts off the life blood of its operation. The LNG received at Cove Point comes from a giant natural gas field at Hassi R'mel, Algeria. It is liquefied at the North Africa port of Arzew, and shipped 4,000 miles to Cove Point aboard a fleet of nine specially designed ships, each the size of the Queen Elizabeth II. The ships unload the LNG at an offshore platform, from where the LNG is pumped through a 6,400 foot tunnel to four storage tanks, each large enough to supply the gas needs of 8,000 homes for a year.

After the LNG is converted back to natural gas, it is pumped 87 miles through a 36-inch diameter pipeline to a measuring station just west of Dulles Airport in Loudoun County, Va. From that point, the two companies that own the Cove Point facility, Columbia Gas and Consolidated Natural Gas, move the gas through their pipelines to customers in seven Eastern and Midwestern states. Between them, they serve 7 million, or 15 percent, of the gas customers in the country. tColumbia's customers include Washington Gas Light and Baltimore Gas and Electric.

Although the explosion hurled debris as far as 300 feet from the electrical substation, the closest of the four LNG storage tanks was 900 feet from the scene.

Beullah Vaillancourt, whose house is across the road from the plant entrance, said the explosion woke everybody, and it was frightening for the moment." Another local resident, retired Army Gen. Henry A. Miley Jr., said the blast "made me a prophet with honor, at last." Miley said that while "it was never in my bag not to have the plant here," he had consistently sought assurances at public meeting that the plant would be "thoroughly and frequently inspected."

Dennis McGee, managing editor of the weekly Prince Frederick Recorder, said while there is "some concern," most residents are philosophical. And Columbia Gas had been "very open" and done a good job of keeping in touch with the community, McGee said.

Typical of the openness was the decision of plant manager Van Dyke to visit residents after the accident and explain what had happened. "He came to us," said Mrs. Vaillancourt, "and we feel there's no real danger, like it's over."

But congressional investigators are not yet satisfied. A subcommittee aide said Markey will ask plant officials to "convince us they know what caused the pump to fail. Industry consensus is that the standards are defective, but it is of little consolation to the relatives of victims that no law has been broken."