SEATTLE (AP) _ Airlines have reported several dozen rudder system problems on Boeing 737s since 1974, including apparent malfunctions of a part that can leak and cause misdirection of a plane, according to a published report.

The Seattle Times said it reviewed 20 years of airline reports submitted to the Federal Aviation Administration and found a series of malfunctions involving not only the 737's rudder part, but its autopilot and other parts that control a plane's flight.

In two dozen cases, jets made unscheduled landings, emergency descents or returned to the gate because of the problems, the paper reported Wednesday.

Boeing officials said the incidents cited in the FAA documents are raw reports. The company said there is no way to determine whether the reported apparent malfunctions are related, and it said no accidents have been attributed to faulty rudder systems.

''These instances cited have neither been thoroughly investigated nor substantiated,'' Boeing spokesman Steve Thieme said.

Rudder malfunction is among the possibilities under study as a cause of a Sept. 8 USAir jet crash near Pittsburgh in which 132 died. Preliminary tests by its manufacturer last week failed to turn up any problems with a rudder Power Control Unit retrieved from the wreckage.

National Transportation Safety Board spokesman Mike Benson said authorities won't draw conclusions about the Pittsburgh crash for months.

The documents the newspaper reviewed, known as Service Difficulty Reports, are one-page reports filed by airlines with the FAA. The Times said it surveyed 550,000 such reports supplied to it by an independent aviation data retrieval firm. The reports are from 1974 though August 1994.

The newspaper found:

- Forty-six rudder system problems on 737 flights, 21 of which the airlines attributed to hydraulic fluid leaks in the rudder part, called a Power Control Unit. Of the 21 incidents, 11 resulted in unscheduled landings, two involved emergency descents and one resulted in an aborted landing approach. In three cases, pilots returned to the gate before takeoff.

- Fifty 737 autopilot malfunctions also were reported, including 17 incidents of uncommanded rudder movements. Eight of those incidents resulted in unscheduled landings.

Boeing's Thieme said there have been more than 54 million 737 flights since the plane went into service in 1968. Asked whether 21 reports of leaky Power Control Units over 20 years is a significant number, he replied, ''I'll leave that for you to determine.''