The thing rises out of the offshore fog like a disconnected piece of a bridge from nowhere to no place. Boatloads of fishermen troll around it, idly watching the workers swarming over the pipes and pilings and huge round columns visible from underneath.

The workers are putting the finishing touches on the half-mile-long offshore loading dock here of the nation's first major import terminal for liquefied natural gas, one of the most controversial fuels there is.

The Cove Point plant has been nine years in the planning, approval process and construction and has cost the Columbia LNG (Liquefied Natural Gas) Corp. $350 million. When it is finished in idle for at least another month with nothing to sell because of construction delays at the supply source in Algeria.

That will cost consumers about $1 million for every month's delay because of interest on the investment which will eventually be rolled into the price of gas. But there is no worry about eventual completion of the Algeria facilities to supercool and liquefy the natural methane. An industry is being born with Cove Point's completion: it and the nine $170 million ships that will serve it are only the first of seven major U.S. LNG projects, and most of them involve Algeria. They could provide 22 per cent of all U.S. gas needs by 1985, according to the respected Pipeline and Gas Journal.

The billions of dollars involved is one of the targets for environmentalists, who complain that the entire LNG industry is just another big-money,low-labor detour on the inevitable road to the use of renewable energy resources like the sun. They warn that LNG use increases U.S. reliance on foreign energy imports, and worry that the huge double-hulled vessels that carry it are floating bombs. A major spill, they say, could create an inmense and devastating fireball.

Industry supporters say that LNG, properly handled, is less dangerous than many things already in everyday commerce, including oil.LNG, they say, is a major fuel available right now that is otherwise being wasted, and they add that it will be an important part of bridging the energy gap until transition from oil to renewable resources is achieved.

The Cove Point plant brought the entire controversy to 1,022 bucolic acres along the Chesapeake Bay, 60 miles southeast of Washington. It provided 900 jobs during peak construction - although only 90 persons will work here when the plant is in full swing. Construction involved 161 federal, state and county permits, including one for the second elevator ever to be installed in Calvert County (the first is in the county courthouse).

The state and local governments stand to gain about $5 million a year in taxes, according to Maryland state personal property supervisor Richard Doolittle, although the bill won't be presented until July, 1979. The Coast Guard has set up a new eight-member marine safety branch office nearyby, primarily to watch over the Cove Point operation.

The main Coast Guard worry is that LNG will somehow spill out of the tankers or the pipelines, vaporize into a gas cloud 600 times the volume of LNG, and ignite. Environmentalists worry about the possible effects of such fire on the Calvert Cliffs nuclear power plant, four miles up the coast.

Industry defenders note that LNG clouds have never exploded in experiments in open air conditions, but only burned. In 15 years of small-scale international commerce and use of domestic natural gas companies as a form of storage, LNG has only spilled and burned badly once; in Cleveland in 1944, when two tanks ruptured. The resulting fire killed 128 persons. Technology has improved vastly since then, industry supporters say, and the Cove Point plant incoporates the very latest.

LNG is simply ordinary cooking gas chilled to 260 degrees below zero Fahrenheit so that it becomes a liquid. It looks like water. Tankers that carry it to Cove Point, like the pipelines and tanks onshore, are not refrigerated but only heavily insulated.

Although ships will initially arrive every 16 to 32 days as the Algeria plants gear up, LNG tankers carrying 750,000 barrels each will be coming through Cheaspeake Bay every 3 1/2 days by the end of 1978, tying up stern to stern two at a time along the offshore unloading dock.

"We feel that on a scale of comparison with oil tankers, these are somewhat safer," said Lt. Cdr. Randolph DeKroney, spokesman of the Baltimore marine safety office of the Coast Guard. He said a detailed study and operation plan would still allow the tankers to move in normal traffic in the lower Cheaspeake since water depth and maneuvering space are ample. LNG tankers entering narrow Boston Harbor channels undergo much stiffer safety precautions.

"Even if we did have a rupture the area covered would generally not affect population areas," DeKroney said. The Coast Guard will enforce all shipboard safety regulations and monitor unloading, he added. Flexible booms will allow unloading even in winds up to 65 miles per hour.

Insulated pipes will then carry the LNG down 40 feet to the bottom of the bay and 1 1/4 miles through a tunnel to shore and four huge 375,000-barrel storage tanks. The three-chambered tunnel (one for each of two pipelines and one access chamber) was a $30 million concession to esthetic objections from the Sierra Club, and environmentalist group, to the original plan for an above-water pipeline trestle.

Rubble was placed over the tunnel area for protection, and sea growth on it has attracted fish, making the area newly popular with anglers, according to Columbia LNG Corp., spokesman Max Levy.

The tanks are each surrounded by dikes that could contain the entire contents in the event of a spill. From there the LNG goes to regasifiers where it is heated back into a vapor . At capacity, Cove Point will be pumping 1.1 billion cubic feet of gas a day into the Columbia mains at Loudoun County, 1 per cent of the total U.S. natural gas use.

The gas will cost $1.89 per thousand cubic feet to Columbia's 4 million customers, who make up about 10 per cent of all U.S. gas users, a company brochure said. Although that rate is well above President Carter's proposed $1.75 limit for domestic interstate gas, it is considered competitive under a complex integrated pricing scheme that is still being debated.

It is probably the cheapest LNG will ever be anywhere, however, since it reflects a 20-year contract negotiated with Algeria in 1971, whent he price there was 34 cents per thousand cubic feet. All contracts since then have been for $1.25 or more per thousand cubic feet. That means that the six other pending LNG projects will be selling - if they can - at $3.50 to $5.50 per thousand cubic feet, according to Frazier King, staff counsel on Cove Point at the Federal Energy Regulatory Commission.

Congress and the LNG industry are awaiting a General Accounting Office study of the safety of LNG due out by the end of the year. A draft copy, Max Levy of Columbia said, is "the most irresponsible thing I've ever seen published by the government." He said it "has a fixation with sabotage and doesn't really discuss regular operating safety . . . it tells you how to blow up an LNG terminal, complete with a bibliography on how to make the bomb."

His reaction typified the industry feeling that it is being pilloried before having a chance of prove itself at places like Cove Point."We didn't blaze any new trails here," he said. "We're using well-proven, standard technology throughout and it will work just fine. You'll see."