Tower controllers at New Orleans International Airport twice broadcast warnings of potentially dangerous winds minutes before a Pan American World Airways jetliner took off and crashed Friday, the National Transportation Safety Board said today.

It is not known whether the plane's pilots received the word to watch out for "wind shear," rapid shifts in wind speed and direction that have emerged as one of the suspected causes of Friday afternoon's crash, the second worst in U.S. aviation history.

The fully loaded Boeing 727 slammed into a residential neighborhood in the New Orleans suburb of Kenner moments after lifting off in a thunderstorm, killing 145 people in the plane and at least eight on the ground.

Disclosure of the tower's wind shear warnings came as investigators began detailed examination of the plane's wreckage. At the same time, workers continued the search for bodies, and Archbishop Philip Hannan of New Orleans presided at a Catholic memorial mass for crash victims.

In Washington, technicians were disappointed to find that the voices of the pilot, copilot and flight engineer had barely registered on the cockpit recorder tape, apparently due to faulty maintenance, safety board officials said. The tapes will be filtered electronically at an FBI lab to try to make the voices and sounds more audible.

In addition, safety board officials said, the voices are obscured by the sound of windshield wipers which were on at impact.

Tonight, safety board vice chairman Patricia Goldman said the voice recorder revealed that copilot Donald Pierce was flying the plane at the time of the accident. She said pilots and copilots routinely alternate flying a plane on different legs of a flight.

Board investigators have not yet decoded the flight data recorder, a second recorder that plots graphs of speed, direction, altitude and vertical forces. Board officials have noted that the recorder is based on 1950s' technology and yields data far less complete and accurate than digital models required aboard wide-bodied planes.

Goldman said that about four minutes before the 727 was cleared for take-off, a controller in the tower broadcast a warning that wind shear had been detected northeast of the airport. One minute later, another warning said that wind shear had been found in all directions.

Both warnings were broadcast on a radio frequency used to direct taxiing aircraft. It was not known whether the Pan Am crew heard and understood the warnings. "They could have been on a different frequency," Goldman said. The cockpit voice tape could answer that question.

Pilots say the warnings do not normally mean that takeoff should be delayed but that the crew should be alert because wind shear can cause abrupt and potentially dangerous shifts in a plane's speed and direction.

Computers trigger wind shear warnings in the tower if wind speed at measuring devices at the airport varies by 15 knots or more with the speed measured at devices outside the perimeter. Detectors have been installed at many U.S. airports in the past five years as understanding of wind shear has advanced.

Investigators stress that it is too soon to pinpoint the crash's cause. But speculation centers on theories that the plane was caught in a violent "downburst" of air in a wind shear and was literally driven to the ground.

Lightning, waterlogged engines, failure of control services and pilot error have been named as other possible causes.

Some investigators now believe that when the jet clipped through tree tops in its descent, it lost lift devices on one wing, throwing it into a steep bank to the left. The left wingtip may have hit the ground first, digging a furrow and throwing the plane into a fiery cartwheel over a three-block area.

At the crash site today, the grim search for victims went slowly.

"We still think there are more bodies in there," Jefferson Parish (county) Sheriff Harry Lee said. "We found a body last night in the middle of the street that thousands of people must have walked right by and not seen."

"We think we have 130 torsos or major portions of bodies," he said. "We have more than 212 body bags." Twenty bodies had been identified by this morning.

Crews also hunted for personal or valuable items among the bits of wreckage, clothing and other debris spread across the area.

Searchers found $11,000 on one body and $4,000 on another, deputies said.

At a hangar at New Orleans International airport two miles away, coroners worked with dental experts from Louisiana State University and FBI agents to reassemble and identify the bodies, a task that could take weeks.

Today, tractors began tearing down the remaining walls of the devastated ranch-style homes in Kenner, as masked workers sprayed disinfectant through the swath of destruction left by the plane.

Local residents expressed anger over the accident. "We knew something like this was going to happen, we just didn't know when," said Wayne Roberts, whose house stands half a block from where most of the wreckage came to rest.

Felix Pourciau, a retired insurance worker, said residents had tried unsuccessfully for years to get the airport to reduce low-level traffic over their homes.

Kenner city councilman John Lavarine said that "noise and fear of the airplanes flying so low over the houses" has been the biggest single complaint he has heard during his time in office.

Earlier in the day, several hundred Kenner residents, including many who had lost relatives in the crash, crowded into a school auditorium for a Catholic memorial mass.

Archbishop Hannan lauded the community's response in clothes and money for those left homeless. Hannan told worshippers that the circumstances of the victims' death were not important. Death "is simply a prelude to our eternal life with Christ," he said.

"God uses wind . . . as a means of proclaiming his presence," he said before prayers were led for the dead, the injured and the rescue teams.