The number of consumer complaints against U.S. airlines fell in December to the lowest level in four years, the Department of Transportation said.

The department also reported Thursday that the on-time performance of the 13 largest carriers in November worsened. The on-time mark had held above 80 percent for seven previous months, including October's 83.4 percent, but fell to 77.7 percent in November.The monthly performance reports also showed a slight increase in November for mishandled baggage, with 6.17 reports per 1,000 passengers, compared with 6.09 a month earlier.

The department said it received 724 consumer complaints about airlines in December, down 40 percent from November and the fewest recorded since December 1984, when the total was 552. For the year, the 23,844 complaints meant a 47 percent improvement over 1987.

Though the complaint statistics are released at the same time as the on-time and mishandled-baggage data, they routinely represent different months, since the complaint figures are more quickly compiled.

Eastern Airlines, which early this year was consistently among the worst on-time performers, had the best record in November, 85.3 percent. Eastern also led October's list, with a 90.3 percent mark.

"On time" means within 15 minutes of scheduled arrival, and the records do not count flights delayed because of mechanical problems.

Eastern was followed by Delta, with an on-time record of 79.8 percent in November, and American West, at 79.2 percent.