Eric von Steinner had just stepped up to the National Airlines ticket counter at Washington National Airport yesterday when a tinny buzzing sound went off from a telephone in front of him.

"Oops, your flight's just been canceled," ticket agent William Bedio told the surprised von Steinner.

For the second day in a row, National Airlines and Pan Am World Airways yesterday canceled flights around the country because of a wildcat walkout of more than 7,500 employes.

Union members were expected to remain off the job this morning, causing further disruptions to airline service at National Airport. An airline spokesman said Pan Am plans to go to federal court next Monday for a second time to seek to end the dispute. The spokesman said he hopes matters will be resolved before then.

The walkout was prompted by Pan Am's dismissal last Wednesday of 16 West Coast workers, members of the Transport Workers Union, a move the airline said was an economy measure and the union charged was a violation of its labor contract.

The nationwide walkout forced cancellation of 122 of National's 135 daily flights, including 13 of 16 flights leaving from National Airport. Pan Am, which merged with National on Jan. 19, also was affected by the walkout, canceling five of its scheduled 185 daily flights.

"You'd think they could notify you ahead of time that your flight was canceled, instead of telling you at the last minute." Patricia Schneider snapped yesterday as she lugged her parents' bags to the Delta Airlines counter at National. Her parents, Francis and Rosemary Riley of McLean, spent the first hours of their long-planned Florida vacation waiting at the airport for a flight south.

National spokesman Merle Richman said that "virtually all National passengers were booked on other airlines" yesterday and that delays were minimal. "We have been hopeful all along that the union would honor a court order to return to work. So far, they haven't," he said.

U.S. District Court Judge Henry Bramwell in Brooklyn Wednesday ordered the airline workers back to their jobs. A union spokesman said yesterday the union was complying with the order but scenes at National and elsewhere indicated otherwise.

For hundreds of passengers at National, however, the wrangling was insignificant compared to their own inconvenience.

"I'm supposed to board an aircraft carrier this afternoon," complained Navy Lt. Cmdr. Phil Marquart, who was trying to get to Jacksonville, Fla. "I'm a little unhappy at this." Marquart was booked on an Air Florida flight that would get him to his ship two hours late.

"I'm probably going to miss a dinner conference because of this," gasped Duke University Prof. Colin Blaydon as he rushed from the National ticket counter to an Eastern Air Lines flight. Like many caught by the dispute, he boarded a flight to Atlanta, saying he "hoped" he could find a connecting flight there that would get him to Florida.

"Actually, this isn't too bad," mused Bob Carlton, international director of the Baptist-oriented Missionary Broadcasters Inc. and station manager of a "gospel Christian" radio station in Brazil. "Once a flight of mine in Manas, Brazil, was cancelled, and I waited a week for another one."

National Airlines was far more gravely affected by the walkout than was Pan Am because all 41 members of National's dispatching staff at the Miami headquarters who are union members walked off the job, according to airline spokesmen.

The Miami dispatchers program computers with key information for all National's flights around the country, then track them from take-off to landing, the spokesmen said, "Without dispatchers you can't fly," said one official.

The 13 National flights that did fly yestereay were dispatched by administrative personnel, according to National spokesman Mike Clark in Miami.