A rail strike affecting most of the nation's railroads left thousands of Washington area residents without rail service to western Maryland, Virginia and the South yesterday and cut freight traffic by half in the Potomac Yards, the Eastern Seaboard's main North-South artery.

After mechanics, engineers, trainmen and other railroad employes refused to cross picket lines set up by striking Southern Railway clerks, supervisors attempted to move trains through the 100 miles of track in the critical Potomac Yards to keep freight moving in the North-South corridor. The 43 supervisors were attempting to fill in for 480 workers who regularly man the Potomac terminal.

Yard Supervisor J. F. McGinley said he was optimistic that the courts would order the workers back to work, but he already was preparing for a war of attrition, hiring a catering service for the supervisors, preparing to put a dining car into operation to serve meals, and looking for shelter for the supervisors.

"We'll have plenty of coffee and food and plenty of room to sleep. We've set ourselves down to stay here for a long time," said McGinley.

It was said McGinley, just like a winter blizzard, only in September. Railroad workers from the midnight to 8 a.m. shift were ordered to work an additional shift to cover for the men who had not crossed the picket line outside.

The workers at the Potomac Yard said labor relations at the yard were excellent, but that they were honoring the Southern Railroad picket line because they were fellow members of the Brotherhood of Railroad Carmen of America, and that they would stay out as long as it took for the striking workers to solve their differences with management.

A picketer at the Potomac Yards, who declined to give his name, said he had been told that the union had recruited more people to augment the handful of pickets at the Alexandria terminal and that they would be arriving within the next day or two.

Inside the yard's main office, workers who had worked through the night and were ordered to work the eight-hour morning shift slouched over their coffee cups, talked of the overtime they were making, and said they hoped the strike would not end shortly.

They receive $12.50 in strike benefits from the union for each day they are out, according to union members.

Freight traffic through the normally bustling Potomac Yards was reduced by half, with only about 2,000 cars passing through the yard yesterday.

Each car holds between $15,000 and $40,000 worth of commodities on the average, and a prolonged strike would have a severe impact on industry nationwide, according to yard supervisor McGinley. With so much steel and so many auto parts travelling the rails, the auto and steel industry would be the first to feel the crunch, McGinley said.

The dispute began 79 days ago when Norfolk and Western Railway clerks went out on strike over questions of union jurisdiction and job security. By yesterday it had spread to 73 other railroads nationwide. Southern Railroad workers went out on strike yesterday morning for a new contract and in support of the striking Norfolk and Western workers.

Amtrak estimated that 14.600 rail travellers nationwide were affected by the strike. A Chessie spokesman in the Cleveland headquarters said the railroad's "communications are so screwed up it's unbelievable," that he had not been able to reach the Baltimore office all day. He said he was uncertain which trains were running and which were not.

A Baltimore Chessie spokesman said its train were running close to schedule after Federal District Court Judge Joseph Young ordered Norfolk and Western picketers to picket only those rail lines involving Norfolk and Western rail service.

Chessie's large terminal at Hagerstown, Md., was relaying on supervisors to handle freight trains. "We're doing the best we can," said a Chessie spokesman.

Passenger and freight traffic moving from Washington to the North and Northeast seemed to be unimpeded by the strike, according to railroad industry spokesman.

Of the 45 long-distance Amtrak trains that regularly arrive and depart from Union Station, 17 either did not reach the Weashington station or did not leave from it.

Passengers were unable to take rail service yesterday from Union Station to any point south or west of Wash- [TEXT OMITTED FROM SOURCE].