The voice and data recorders from EgyptAir Flight 990 reveal that just before one of the pilots, apparently alone in the cockpit, turned off the autopilot, he uttered a very short Muslim prayer, government sources said. National Transportation Safety Board officials found the evidence so disturbing they are considering turning the probe over to the FBI.

Investigators are certain what the words in Arabic were, the sources said, but they aren't sure how to interpret their meaning.

The cockpit voice recorder tape also contains sounds similar to a door opening and closing more than once, the sources said. That led investigators to wonder whether one of the pilots left the cockpit, which would have given the other pilot the opportunity to take some action that could have led to the Oct. 31 crash, which killed 217.

Although it is far from certain, one highly placed source said the captain apparently had been out of the cockpit and returned just as the plane's fatal dive began, and after that "there is some evidence they are working at cross purposes."

The new information came after NTSB technicians synchronized the voice and flight data recorders and Arabic translators listened carefully to the tape. FBI Director Louis J. Freeh and NTSB Chairman Jim Hall met yesterday to discuss what both agencies know about the two tapes and how to proceed.

A high government source said the government wants to officially inform the Egyptian government and still wants native Egyptian Arabic speakers to hear the tape to be certain, but "all signs are pointing" toward giving the case to the FBI to investigate as a criminal probe.

The tone of the investigation changed overnight. A day ago, the FBI was saying with certainty that no evidence of criminal acts had been found. And numerous federal law enforcement and political sources, who Sunday night said a preliminary reading of the Boeing 767's voice recorder contained no indication the plane was deliberately crashed by someone in the cockpit, are now not so sure.

Language specialists from the CIA joined the group analyzing the voice recorder tape yesterday, even as some senior NTSB investigators, the Federal Aviation Administration and Boeing Co. have been denied normal access to the tapes and security at the safety board's laboratory in Southwest Washington was heightened.

Hall refused to offer substantive answers to any question at an afternoon briefing yesterday, but expressed confidence that the cockpit voice recorder and flight data recorder would allow the agency to solve the mystery of why the plane went into a sudden dive from 33,000 feet and plunged into the Atlantic.

"Let me be quite clear on where this investigation is tonight," Hall said. "We are concentrating our efforts on determining from the evidence, including the CVR, whether or not this investigation is to remain under the leadership of the NTSB."

Hall refused to clarify his statement under pointed questioning.

Under safety board procedures, the FBI immediately takes over a crash investigation when there is some evidence of criminal conduct; the safety board then declines to comment and aids the FBI investigation.

It is highly unusual for the safety board to clamp down on information. The board prides itself on releasing daily any confirmed information even if it is not yet fully in context. That effort is to assure the public that there is no substantial information they do not have, and therefore discourage rumors and conspiracy theories.

Government sources said the words on the cockpit recorder that disturbed investigators were not noted on a first hearing of the tape. But after the tape had been refined and heard by a translator fluent in the particular Arabic dialect, the translator immediately reported its significance to investigators.

The key to understanding the sequence of events was that the safety board laboratory was able to correlate the exact timing on the cockpit voice recorder and the flight data recorder. They therefore knew exactly when the troubling words were uttered and when the door was opened, in relation to the plane's dive.

Cockpit voice recorders on modern aircraft are sophisticated sound systems with four microphones strategically placed around the cockpit. If the recorder works properly, it will catch even the most subtle sound. The safety board's laboratory can analyze almost any sound, even determining exactly how fast an engine was running outside and what sort of explosive was used in terrorist acts.

According to the two recorders, Flight 990 had an uneventful climb to its cruising altitude on its way from New York to Cairo with Capts. Ahmed Habashy and Raouf Noureldin at the controls.

At 45 seconds after 1:49 a.m., the autopilot was disconnected, apparently by one of the pilots. Eight seconds later, the plane began a pilot-initiated dive that gradually increased over the next 10 to 12 seconds.

About 15 seconds later, two odd things happened. The left and right elevators on the horizontal stabilizer--which make the plane go up or down--moved in opposite directions. Normally, they move in tandem, but they can move independently if one pilot pushes forward on his control column and the other pilot pulls backward.

Also, someone shut off the two engines by pulling the engine start levers to "cutoff."

Whether these actions resulted from a struggle would be one focus of a criminal investigation.

On long overseas flights, three and sometimes four pilots are used to allow everyone to have rest breaks. Although it is not clear where two of the four EgyptAir pilots were located at the time of the dive, it would be normal after reaching cruise altitude for one or two of them to go to rest areas to be fresh for later phases of the flight.

After the engine shutdown, power went off to the recorders and the altitude-reporting transponder, but a radar analysis indicates the plane climbed to 24,000 feet and then apparently stalled and fell to the ocean. Pilots point out that a fast-moving plane likely would climb abruptly if all controls are relaxed.

Conspiracy theories abounded in the crash of Trans World Airlines Flight 800 in 1996 partly because the FBI effectively took control of the investigation--even though it was never declared the lead agency--and the flow of information was restricted.

Regarding Flight 990, the FBI had repeatedly said publicly and privately--as late as Sunday night--that there was no evidence of criminal activity. There were no such assurances yesterday, however.

"We are reviewing the tape to determine if we have jurisdiction. Right now there hasn't been a determination," said FBI spokeswoman Anita Dickens. "We are not the lead agency as of now. There have been a lot of meetings."

Staff writers Lorraine Adams and Vernon Loeb contributed to this report.