SEATTLE (AP) _ The Air Line Pilots Association said Wednesday its probe of a Delta jetliner crash at Dallas in August has prompted it to seek an emergency modification in takeoff warning systems of all Boeing 727 jetliners.

The union, which represents commercial jet flight crews, said it had found a ''serious deficiency'' in the lack of an inboard wing flap position sensor for the stall warning system on 727s.

Salt Lake City-bound Delta Flight 1141 crashed and burned while taking off from Dallas-Fort Worth International Airport on Aug. 31, killing 14 of the 108 on board the Boeing 727.

The National Transportation Safety Board said that while Flight 1141 had no problems as it rolled down the runway, it encountered almost immediate trouble after liftoff and rolled violently from left to right before crashing.

As part of its investigation into the crash, the NTSB has studied whether the takeoff warning system alarm failed on the Delta flight. The alarm is designed to sound if a pilot has not prepared an aircraft properly for takeoff, such as leaving wing flaps, which help give a plane lift, in the wrong position.

The ALPA on Wednesday released a letter to LeRoy A. Keith, manager of the FAA's Aircraft Certification Division in Seattle, from Harold F. Marthinsen, director of ALPA's Accident Investigation Department.

In it, Marthisen noted that the flap position sensor on a 727 is located on the outboard wing flap, but not on the inboard flap.

If the outboard flaps were properly extended for takeoff, but the inboard flaps were still retracted, Marthisen said the warning alarm would not sound.

''While the NTSB has yet to explore this possible explanation for the accident, the Air Line Pilots Assocation accident investigators feel strongly that there is sufficient evidence to conclude that such a condition did exist on the accident aircraft,'' Marthisen wrote.

''Even if this was not the cause of the Delta accident, such an occurrence could be the cause of another one,'' he wrote, urging the FAA to issue an emergency directive to correct the B727 stall warning system.

Dave Duff, FAA spokesman in Seattle, said the region's Aircraft Certification Division has started investigating the factors mentioned in the letter.

He said the FAA plans no action before NTSB hearings on the Delta crash begin in Dallas on Tuesday.

Michael Benson, spokesman for the NTSB in Washington, D.C., declined comment on the ALPA letter, but noted that the stall warning system will be a subject of the NTSB hearings. Benson said ALPA is a party to the hearings and can question witnesses about the system.

Boeing Commercial Airplanes spokesman Jack Gamble likewise declined comment because the stall warning system will be discussed at the NTSB hearing.

In September, the FAA as a precaution ordered operators of 727s to check the takeoff alarms. The agency announced Oct. 20 that in 35 of approximately 1,200 727s examined, the alarms either did not work or worked improperly.