Pulled by gravity's invisible hand, one of 7,071 waiting coal cars at Norfolk & Western's coal port glided down ice-cold railroad tracks into the thawing shed, a giant toaster of a building with infrared heaters up and down its sides.

Out the other end, the coal-heaped hopper car pushed through a veil of rubber strips, continuing down the rails to a rotary dumper. With the railroad car inside, the giant cylinder rolled over and began shaking loose the frozen coal.

The frigid weather that left Washington at an ice-slick near standstill in January was slowing down the coal pipeline, the system that moves coal from the mines to anxious and waiting customers in Europe and Japan.

A year ago that system seemed in danger of fatal overload. This year, except for problems related to near-paralyzing cold, the system is working relatively smoothly.

In 1980, heavy demand compounded by an unusual convergence of international events overworked unprepared railroads, shippers and port facilities. Strikes in other coal producing countries, on top of the interruption in supplies of crude oil from Iran and higher oil prices by the Organization of Petroleum Exporting Countries, combined to produce a bonanza for the American coal industry that became a massive headache for it as well.

At the worst point, 100 to 160 colliers were anchored in the Chesapeake Bay and delays in loading were as long as 60 days, while shippers paid an average $15,000 to $20,000 a day in waiting charges.

It was a time of both maximum opportunity and maximum threat for the East Coast ports, Hampton Roads and--to a lesser extent--Baltimore Harbor, which are the funnel through which nearly all of the nation's coal exports flow.

"Everybody was grabbing up clerks and labor off the streets. We had to function. We didn't have time to plan," said T. Parker Host Jr., chairman of the Hampton Roads Maritime Association. "It just caught us all off guard."

"If we still had 160 ships and people waiting 50 to 60 days, people wouldn't be looking at Hampton Roads. They would be looking at any little port," said Richard Counselman, president of the Virginia Pilots Association.

During the last several months of 1981 only 15 to 20 ships sat at anchor in Hampton Roads, according to maritime officials. Even when ice clogged the coal transportation pipeline in January, the number was only 40 to 45. One major factor in improving the pipeline has been systems adopted by the railroads to ensure that ships and the coal they were there for arrived at the same time.

In the chaos of 1980, almost everyone seemed to be planning a new coal pier. Proposals for coal piers popped up in any city with a port and all around the edges of the Chesapeake--the Persian Gulf of coal, according to Fortune Magazine. Now, with the old facilities undergoing expansion and working better, second thoughts are setting in.

Many proposed facilities, including some in Hampton Roads and Baltimore, will not be built, Maryland and Virginia authorities predict.

"Why should you go somewhere down the road and build a pier when Baltimore and Hampton Roads are carrying 90 percent of the coal?" said Hans Mayer, chairman of Governor Harry Hughes' Export Coal Task Force. "I can't believe reasonable people will make those kinds of investments knowing they are already late."

Right now Baltimore has a capacity to ship approximately 18 million tons of coal a year and expects to handled approximately 14 million. In addition, a 10 million ton facility being constructed by Island Creek Coal Co. at Curtis Bay is scheduled to be complete in 1983. Another facility that will handle 12 million tons and can be expanded to 20 million is being built by Consolidation Coal in Canton and is supposed to be complete by the end of this year, said Mayer.

Two more projects have been proposed, one of which appears unlikely to be built. Five companies had planned a coal project at Marley Neck that could handle 15 million tons annually, but four of the companies have withdrawn from the venture.

More likely, in the view of state officials, is a facility that will use an iron ore import pier at Bethlehem Steel for coal export. That facility will handle approximately 6 million tons. If all but the Marley Neck project are built, Baltimore's capacity will be more than doubled within a very few years.

In Hampton Roads, the A. T. Massey Co. plans a 12 million ton facility at Newport News to be complete late this year. Dominion Terminal Associates, a consortium of Westmoreland Coal Co., Armco Inc., Ashland and Utah International Coal, plan a 15 million ton facility. M. Shawver Associates Inc. has begun work on a 3 to 5 million ton project expected to be complete by late spring.

The state of Virginia also plans a coal pier that could handle 25 tons, but that project faces several obstacles. Six coal companies that would use the facility say they must have discounts from the railroads if they are to use the facility. Getting it built also requires overcoming resistance from the communities through which railroad tracks would cross.

The proposed facilities would more than double capacity at Hampton Roads, which loaded 47 million tons of coal last year.

Coal exports have risen from 40 million tons in 1978 to 65 million tons in 1979, 90 million tons in 1980 and 110.6 million tons in 1981. The forecasts are for exports as high as 215 million tons by the year 2000. Hampton Roads and Baltimore Harbor expect to handle most of that and to prosper.

The stakes for Maryland and Virginia in continuing to handle most of the nation's coal exports are big. In Maryland, an estimated 2,500 jobs depend on coal exports right now. With the improvement in facilities, that figure is expected to rise to more than 5,000 jobs. The dollar impact on the state will amount to approximately $240 million in 1980 dollars, according to Mayer. "That's pretty heavy stuff."

In Virginia, each ton of coal exported leaves behind an estimated $19 to $20 in benefits to the state, said T. Parker Host Jr. That adds up to $893 million to $940 million in benefits to the state in 1981.

"When we had 150 ships out there, everybody thought if they had a crane and a barge they could load some of those ships," said Counselman of the Virginia Pilots Association.

In 1980, even with the difficulties, Hampton Roads handled 70 percent of the nation's coal exports. In 1981, it handled 60 percent, with New Orleans picking up most of the percentage that Hampton Roads lost.

In the past year, both Hampton Roads and Baltimore have worked on improving facilities and procedures for coal export. An increasing amount of the coal exported is steam coal, used to fuel utilities, rather than metallurgical coal used in steel production. That will require some changes in facilities.

A 10-week United Mine Workers strike in 1981 gave the railroads and others time to figure out how to handle the increased volume and to do maintenance work. Norfolk & Western began using two types of contracts. One type of contract sets timetables for everyone involved along the pipeline and makes anyone who causes a delay pay. Mining companies, the railroads and shippers all may find themselves liable for damages if they don't perform on time. Another type of contract, also used by the CSX Corp. (an amalgamation of the Chessie System and Seaboard Coast Line), allows ships to take a number rather than having to sit at anchorage to maintain their position in the queue.

Coal has been a boon and a blessing for the railroads. With general merchandise shipping down, the upsurge in coal handling has helped offset the impact that the economy's slide would have had on the railroads. Both Norfolk & Western and CSX handled more coal in 1981 than in 1980 in spite of the long UMW strike.

"Since we had the strike and the shakeout, people are coming back to Hampton Roads for reasons that made it the biggest coal port in the first place," said Counselman. The reasons include proximity to the Appalachian coal fields, a relatively deep harbor and the facilities of the Norfolk & Western Railroad and the CSX Corp.

"The marketplace established it as dominant," said Jack W. Mace, director of the Hampton Road Maritime Association.

"We don't see ourselves competing with Hampton Roads," said Hans Mayer. "They're dominant, but the market is big enough for both of us."