A man was shot and wounded by a Greenbelt police officer last night in a crowded department store after a woman was stabbed and critically injured while shopping there, authorities said.

The woman, Doris Robertson, 24, of Upper Marlboro, was flown by Maryland State Police helicopter to the shock trauma unit of Prince George's General Hospital, where she underwent surgery late last night for multiple stab wounds, primarily in her back. She was listed in critical but stable condition early this morning.

Her alleged assailant, a 23-year-old man whose name was not released pending notification of relatives, was taken by ambulance to the hospital and also was reported in critical but stable condition.

No one else was injured, officials said. The motive for the stabbing remained unclear and details of the event were sketchy early this morning.

Authorities said the incident occurred about 8:30 p.m. inside Marshall's department store at Beltway Plaza on Greenbelt Road, when a man approached Robertson from behind and began stabbing her repeatedly.

Greenbelt police spokesman Pat McAndrew said a uniformed officer responding to cries for help from other patrons and store employes "called several times for the suspect to stop stabbing, and when he refused to do so, the officer fired one shot" from his service revolver.

A woman who answered the telephone at Marshall's last night identified herself to a reporter as the manager but declined to give her name or comment on the incident.

"As you can imagine, the place was packed at 8:30 on a Saturday night," McAndrew said.

Crowds of shoppers gathered outside Marshall's after the incident, which brought numerous police cars, ambulances, fire equipment and the rescue helicopter to the scene.

"Everyone was kind of stunned, trying to figure out what the helicopter was doing there," one shopper said.

Greenbelt police said the officer involved in the shooting, whose name they declined to release, was placed on administrative leave pending completion of their investigation into the incident.