A Washington-based FBI agent assigned to an antiterrorist task force plunged to his death yesterday in a fall from a helicopter during a training excercise at the bureau's Quantico training academy, FBI officials said.

James K. McAllister, 34, a 16-year veteran of the FBI, was participating in hostage rescue training maneuvers with the agency's elite 50-member Hostage Rescue Team when the accident occurred at 10 a.m., according to FBI spokesman Lane Bonner.

Bonner said there was no link between yesterday's training exercises and threatened retaliations against Americans for the U.S. attack on Libya on Monday.

McAllister fell an estimated 40 to 60 feet during a "rapid-descent exercise," said Bonner. During the exercise, in which agents are trained to reduce their exposure to gunfire, the trainees were supposed to slide down a rope attached to the helicopter.

Bonner said initial reports that McAllister lost his grip in the windy weather were speculative. He said the FBI is still investigating the cause of the accident. McAllister was pronounced dead at Potomac Hospital in nearby Woodbridge shortly after the accident.

FBI Director William H. Webster, in announcing the death, said that the goal of the hostage rescue team "is to save lives. Special Agent McAllister gave his life while preparing himself to save the lives of hostages. He will be sorely missed."

Webster said the team "gives us an effective civilian response capability and provides a substantial deterrent to terrorism."

McAllister was the third FBI agent to die in the line of duty in a week.

Two FBI agents were killed and five were wounded last Friday in a Miami suburb when they engaged in a shootout with two men suspected in a string of bank and armored car robberies. The two suspects also were killed.

"So quickly after the tragic events of last Friday, public attention is focused on the dangers that law enforcement officers face each day," Attorney General Edwin Meese III said in a statement yesterday. "Our burden of sorrow is no lighter when one of our agents dies in an accident than when one dies in a violent confrontation with armed criminals."

McAllister joined the agency as a support employe in 1970 and was promoted to special agent in 1976. He and his wife Kimberly, also an FBI agent, have two children.

McAllister, an original member of the three-year-old hostage rescue team, was assigned to the Washington field office after stints in Baltimore and New York.

The team conducts its training exercises at the FBI Academy at Quantico Marine Base. Bonner said members of the hostage rescue team divide their time between training programs and investigations.

"Director Webster doesn't want them to lose their ability to become investigators," Bonner said. "They still have to be able to do crime scene investigations and interviews."