The nation's 12 largest airlines improved their on-time performances in February while logging fewer passenger complaints, the Department of Transportation reports.

The airlines' on-time record - defined by the agency as arriving within 15 minutes of a scheduled arrival time - improved to 81.8 percent in February, well above the January rate of 73.2 percent, according to the government's monthly report on air travel performance.A year earlier, the on-time rate was 73.2 percent.

Leading the pack in February was American Airlines, whose aircraft arrived on time 88 percent of the time, followed by Pan American, USAir, Delta, Northwest, Continental, America West, Alaska Air, United and TWA.

Southwest Airlines had the worst rate of the airlines studied in the month, with 69.1 percent of its flights arriving on time.

But when measured against data beginning in 1987, America West was out in front, with an arrival rate of 84.0 percent. Following, in descending order, were: Southwest, American, now-defunct Eastern, Alaska Air, Northwest, Delta, Continental, Pan Am, USAir, TWA, United and, alone at the bottom, Midway, which filed for Chapter 11 federal bankruptcy protection from creditors last week.

Complaints about mishandled baggage, meanwhile, dropped to an average of 5.62 per 1,000 passengers flown from 7.89 in January.

America West logged the most baggage complaints, with 8.82 per 1,000 passengers, followed by Alaska Air, United, Delta, Northwest, TWA, USAir, Midway, Southwest, Pan Am, Continental and American, whose passengers complained at a rate of 4.64 per 1,000 passengers.

Other complaints totalled 644 in the month, a 19 percent decline from the 794 complaints registered in January and 30 percent below the 921 recorded in February 1990.

Delta recorded the fewest with a rate of 0.27 per 100,000 passengers, followed by Southwest, USAir, Northwest, Continental, United, American, Pan Am, America West and TWA, whose passengers logged 7.45 complaints per 100,000 passengers.