The Department of Transportation reports a big decrease in the number of passengers denied boarding - bumped - by United States airlines in 1990. Last year, the airlines registered 68,560 denied boardings, or 1.55 per 10,000 passengers, compared with 106,765, or 2.59 per 10,000, in 1989, according to the department's air travel consumer report.

The report advises consumers who want details for on-time performance on specific flights to call airline ticket offices or travel agents whose computerized reservation systems include this information.The department maintains a flight-data file covering more than 20,000 flights that is available for inspection in Room 4201 of its headquarters building at 400 Seventh Street S.W., Washington.