The fatal shooting of a drug suspect by an undercover police officer on Monday was an accident that occurred after the suspect startled the officer, Fairfax County police said yesterday.

The police department's findings that "an unintentional reflex" caused the officer's gun to discharge will be forwarded to the county's chief prosecutor, who will decide whether the shooting was a criminal violation.

Police said the officer, Investigator Irene M. Boyle, will remain on administrative leave pending the prosecutor's review.

"This was strictly an accident," Col. John E. Granfield, chief of police, said yesterday. "She fired it but without any intention of having it fired."

Police, who could not identify the man on Monday, said yesterday that the victim was 27-year-old Jose Carlos Rodriguez of no fixed address. They said the difficulty in identifying Rodriguez stemmed from his prior use of seven aliases and six birthdates.

Police said investigators had negotiated to purchase two ounces of cocaine from Rodriguez for $2,700 and planned to meet him late Sunday in the parking lot behind a dry cleaners in Baileys Crossroads.

Rodriguez drove to a dark section of the parking lot in his rented pickup truck, and an investigator agreed to purchase one ounce of cocaine, all that Rodriguez had with him, police said.

The investigator then alerted other officers in marked and unmarked cruisers, police said. They said Boyle, an 11 1/2-year veteran of the department, walked to the truck with her weapon drawn to provide coverage for another officer.

At first, Boyle did not see Rodriguez, but as she came within a foot of the truck his face suddenly appeared at the window of the cab. "He kind of came up like a jack in the box," said Granfield. "It startled her, and she shot the gun."

Police said one bullet struck Rodriguez in the head, and he was taken to Alexandria Hospital, where he died a short time later. No weapon was recovered from Rodriguez's vehicle, they said.

Had the transaction not gone awry, police said they would have charged Rodriguez with possession of cocaine with intent to distribute, a felony.

Granfield said yesterday that the actions by Boyle, 33, were in accordance with police procedures.

That Boyle had her service revolver "out and drawn" was proper procedure, Granfield said. He noted that in virtually every undercover drug arrest made by county police, the suspects are heavily armed.

Generally police department policy states that deadly force shall not be employed except as a last resort, but Granfield said Boyle had no intention of shooting the weapon.

Commonwealth's Attorney Robert F. Horan Jr. said yesterday that he will review the autopsy results and the findings of the police department's investigation, which was conducted jointly by the homicide department and the internal affairs section.