A 29-year-old Southeast Washington man was shot in the back while at the wheel of his moving car by an undercover D.C. police narcotics investigator yesterday after the man's car allegedly dragged the officer by the arm through a crowded parking lot at National Airport.

Five parked cars were damaged in collisions during the dramatic rush-hour incident, which is under investigation.

The investigator, Roger Isaac, was attempting to question the motorist, who had just gotten off the Eastern Air Lines shuttle from New York, shortly before 4 p.m., according to officials. Isaac, assigned to the U.S. Drug Enforcement Administration task force, had placed his arm through the window of the car on the driver's side to show his identification to the driver, Eugene Alonzo Glascoe, officials said.

Glascoe was listed in fair condition last night at National Orthopaedic and Rehabilitation Hospital in Arlington after undergoing surgery. Isaac was treated for a knee injury at Arlington Hospital and released.

The incident began after Glascoe left the main terminal and walked to Lot 2-C near the Metro station, according to David Hoover, a DEA spokesman. Glascoe got into a blue late-model Buick Regal bearing Michigan license plates.

Isaac, who had followed Glascoe through the terminal and into the parking lot, approached the auto as Glascoe was starting the engine, Hoover said.

The officer, wearing street clothes, took out his identification and, standing next to the car window, held it up for Glascoe to see, according to Hoover.Glascoe then showed the officer his own identification and asked to see Isaac's identification a second time, Hoover said.

When Isaac again displayed his identification, this time stretching his arm through the open car window, officials said the window of the car suddenly rolled up, pinning the officer's arm.

As the vehicle began to move, officials said, Isaac drew his revolver and before he could be dragged 100 feet, shot Glascoe once in the back. Before the car came to a halt it had collided with five other cars parked in the lot. The cars were unoccupied and damage to them was decribed as minor.