Anna Mejia said she thought she would be on the way to Guatemala yesterday. Instead, she was planning to spend the night at home in Silver Spring, one of 43 passengers "bumped" from Pan American Flight 541 at Dulles International Airport yesterday because the flight was overbooked.

"I'm very upset," she said while waiting with a score of other displaced passengers in the airport mezzanine as harried airline employes tries to find them alternative flights.

As it turned out, according to Pan Am regional manager Richard Carlson, all 43 passengers were rescheduled on alternative flights that will arrive in Latin America by Sunday, and each passenger was given a check worth double the cost of the over-booked flight. The remuneration is required by law when a passenger with a reservation misses a flight because it is sold out.

That still failed to please some passengers. "We paid $50 for a cab to get here," said Mauricio Menjivar, who was on his way with his father to El Salvador for Christmas. The Menjivars, however, eventually settled for tickets on a Sunday flight and dutifully took a cab home, looking exasperated.

Carlson, who went to Dulles from his Washington office to supervise the busy rush of holiday travelers, said the flight is normally overbooked. It still leaves with empty seats, according to Carlson, because many passengers fail to show up for a flight although they have reservations. "It (the overbooking) was not a foul-up," he said absolving the often-blamed computer.

Menjivar said he did not care what caused the overbooking, but that he did care if it occurred again. "We've made a reservation for Sunday, but we're not sure what will happen," he said glumly. "Look what happened today."

"They will get there by Christmas," a weary CarlsonSaid.