The number of passengers with "confirmed" reservations who were "bumped" from flights last year totaled 146,618 an increase of more than 15,000 over 1975, according to the latest Civil Aeronautics Board report.

The board said 137,020 passengers were denied boarding on domestic flights by the certified airlines for a rate of 7.5 for every 10,000 persons boarded. A total of 9,598 passengers were denied seats on the carriers' international flights for a rate of 7.1 for every 10,000 passengers boarded.

Among the major airlines, Eastern Air Lines had the best record in 1976, bumping passengers at a rate of 2.1 per 10,000 boardings; National Airlines was next with a 2.3 per 10,000 boarding rate. The major carrier with the worst record last year was Pan American World Airways, which bumped passengers at a rate of 15.4 per 10,000 boardings; Western Air Lines was the next worst with a 14.5 per 10,000 boarding rate.

Under CAB regulations, an airline bumping a passenger with a confirmed reservation must either deliver the passenger to his destination within two hours of the original flight's arrival time (four hours if it is an international flight) or reimburse him for the full value of the flight, up to $200, in addition to letting him keep and use the original ticket.