CIA personnel on a U.S. surveillance plane did not attempt to read the registration number on the side of a civilian aircraft before it was shot down by the Peruvian Air Force on Friday because they were afraid it would flee out of Peru if they got too close, U.S. officials said yesterday.

An American missionary, Veronica "Roni" Bowers, and her 7-month-old daughter were killed when, according to American accounts, the Peruvian Air Force rushed the procedures established by both countries to distinguish drug trafficking flights from innocent aircraft.

Those procedures require Peruvian pilots to identify a plane before attacking it. But the practice during hundreds of U.S. surveillance missions has been for American personnel to fly close enough to obtain a suspected plane's registration number before a Peruvian military jet is ordered into the air, U.S. officials said.

As the Bush administration prepared to send a team of top officials to investigate Friday's mistaken attack, the United States yesterday suspended all its drug surveillance flights in Central and South America while officials reassess the rules they follow.

U.S. officials previously raised concerns with their Peruvian counterparts after a Peruvian jet, using American intelligence information, shot down a private aircraft in 1997 without following safety procedures established by both countries to govern their joint drug interdiction efforts.

Though the aircraft downed in August 1997 proved to be a drug plane, the CIA quickly launched an "intensive dialogue" with Peruvian officials out of fear that providing American radar data could end in tragedy, according to a former State Department official who was posted in Peru at the time.

In the 1997 incident -- one of nearly three dozen cases in which Peruvian jets shot at, forced down or strafed suspected drug planes since 1995 -- the Peruvian Air Force hurried through the precautionary steps and failed to fire warning shots, the former State Department official said. After the plane was downed, military personnel determined that the plane had been used for narcotics trafficking.

"Because it was a drug flight, it wasn't a disaster," he said. "But people realized an accident could happen. . . . Everyone realized we had a problem and we had to get this sorted out quickly."

The incident prompted CIA and other U.S. officials to pursue the issue with top Peruvian officers and those operating in the field. U.S. officials required the Peruvians to read and sign statements that they had reviewed all the procedures for interdiction operations, the intelligence official said. Training sessions also were conducted twice a month to ensure that Peruvian pilots understood the rules of engagement.

"We wanted to make sure the Peruvians not only acknowledged the standard operating procedures at the upper levels but made sure these were communicated to the middle and lower levels," the former State Department official said. He added that Peruvian and American officials were aware that they had to prevent a repeat incident, since inadvertently downing a civilian plane could disrupt joint efforts at combating drugs.

The American program of sharing radar and other intelligence information with the Peruvian Air Force began in 1995 under the Clinton administration, which assured critics in Washington that the assistance would not lead to innocent casualties. Initially the operations were run by the CIA and the U.S. Customs Service. But for most of the time, they have been conducted exclusively by the CIA using contract personnel and aircraft owned by the Department of Defense.

State Department spokesman Richard Boucher said yesterday that the joint interdiction effort had never resulted in harm to innocent civilians before the Friday incident. "It's a terrible tragedy and a horrible occurrence, but this is the first time something like this has happened," he said.

Boucher said U.S. officials would be sent to Peru to investigate the incident in cooperation with Peruvian authorities. "We'll try to get to the bottom of this matter so we understand how to make sure this never happens again," he said.

Sen. Bob Graham (D-Fla.), vice chairman of the Senate Select Committee on Intelligence, cited a wealth of "conflicting facts as of this evening on this case" and said the panel hoped to resolve those discrepancies during a closed door briefing today. "Until we've gone through that process, I think it's not constructive and premature to try to speculate on what the U.S. role was and what kind of policy implications flow from that role," Graham said in an interview.

The decision of the crew on the CIA's Citation surveillance plane not to approach the missionary aircraft and observe its registration number underscores one of the main challenges facing the anti-narcotics missions. While more than 30 smuggling flights have been intercepted in the last six years, far more suspicious planes have escaped over neighboring borders to Colombian and Brazilian airspace, where neither Peruvians nor Americans can follow.

In Friday's case, the crew of the CIA plane made a decision not to approach close enough to the missionary plane to read the registration number clearly painted in big black letters on its side.

"The reason they didn't go close was that, if it was a bad guy, they didn't want to give it a chance to go over the border before the interceptors showed up," a U.S. official said.

Rather than delaying the order for a Peruvian A-37B interceptor jet to take off, the Peruvians assigned the task of identifying the suspect plane to the jet pilot himself.

But a former CIA pilot familiar with these missions said this was unusual. "I do not know of a single instance where a daytime intercept was performed and the Citation crew did not get the registration number prior to a decision to launch an interceptor airplane," he said.

During daytime operations, the American crew ordinarily uses zoom lenses on cameras located in the belly of the Citation to view the number. The information is then communicated to the ground station -- first in English by the Americans and then in Spanish by the Peruvians, according to officials familiar with the missions.

The former pilot said the situation is sometimes different at night, when infrared equipment aboard the surveillance plane is unable to distinguish the registration number and the jet pilot must read it himself.

Shortly before firing on the missionary plane, the Peruvian pilot observed its registration number and radioed it back to a Peruvian liaison officer aboard the U.S. plane but he did not call it into ground commanders for verification, according to an American intelligence official.

Once the military jet was airborne, the American crew began to notice that the plane they were tracking was not behaving like a standard drug flight. The missionary's Cessna was flying too high, on too steady a course, and making no attempt to hide itself or head for the border. The crew tried to get the attention of a Peruvian Air Force liaison officer on board the CIA flight, but he "was talking" into the radio "and not listening," a U.S. official said.

"There was a fluid conversation going on" inside the aircraft, the official said. One American kept trying to ask the Peruvian, "Are you sure? Are you sure? It doesn't look like it to me."

"They questioned him repeatedly," the official said. "The problem is, once the interceptor shows up, it's now an interdiction operation. The commander [of the mission] is now the commander of the Peruvian Air Force. . . . Our guys become a taxi service at this point."

In a radio communication overheard by a U.S. Customs Service P-3 Orion electronic-intelligence gathering plane over Colombia at the time, the American crew then contacted the CIA directly in Lima, asking that the shoot-down be stopped.

The American crew "is absolutely destroyed by this," one official said. "They didn't want it to happen. They didn't have control over it any more."

Staff writers Vernon Loeb and Robert Pierre and special correspondent Gigi Anders contributed to this report.