FBI agent Robin Ahrens, a former Culpeper, Va., teacher who completed training only three months ago, was shot and killed in Phoenix by two fellow agents who mistook her for a robbery suspect's girlfriend, the city's police chief, Ruben Ortega, said yesterday.

The shooting occurred Friday during an arrest when Ahrens, the first female agent to die in action, stepped into a dimly lit passageway with a drawn gun, Ortega said.

Jack Smythe, a spokesman for the Phoenix FBI office, said yesterday he "cannot and will not" comment until the investigation is complete. An assistant FBI director and six investigators arrived in that city late Saturday to conduct the inquiry, which officials said will not be completed before Wednesday.

Phoenix police, meanwhile, are conducting their own investigation. Ortega said he decided to comment on the case after FBI officials refused to release any details.

According to reports from the FBI and the Phoenix police, Ahrens, 33, went with about a dozen agents to a Phoenix apartment complex about 11 p.m. Friday to arrest Kenneth Don Barrett, 27, a Nevada robbery suspect described by the FBI as a "red-hot fugitive -- armed and extremely dangerous."

Barrett emerged from what officials described as his girlfriend's apartment in the Silver Creek complex at 43rd Avenue and Peoria Street. While FBI officials were subduing him, two agents saw Ahrens and opened fire. She was struck at least once in the face and once in the right arm, Phoenix police spokesman Brad Thissam said.

Ahrens was treated by paramedics at the scene, then flown by helicopter about 10 miles to the St. Joseph's Hospital and Medical Center in Phoenix, where she arrived at 11:28 p.m., Phoenix police said. A hospital spokeswoman said Ahrens was not operated on because doctors could not stabilize her condition for surgery.

She died at 5:40 a.m., the 27th FBI agent killed in the bureau's 77-year history, and the first since 1979. Nearly 400 of the bureau's 7,800 agents are women.

Ahrens' friends, sometimes crying as they spoke, described her as an unusually self-confident and able woman who once led a group of teen-aged women on a 40-day canoe trip through the wilds of northern Canada, from the Saskatchewan border through Manitoba to Hudson Bay.

"She knew her character inside out," said Jennifer Campbell, 35, a friend from Winnipeg. "To do something like that, you have to be a survivor, you have to know yourself. For a lot of people, that would put a fear in them. In Robin, it was a challenge. It was like the FBI."

Ahrens also was an avid jogger, photographer, a former swimming pool manager and teacher. From 1980 until the fall of 1984, she worked at the Culpeper County High School as a media specialist, media teacher, assistant librarian and ROTC chaperone.

Friends and acquaintances said she was stubborn, but sensitive and always honest. Joining the FBI was a dream she had had for several years, but she almost gave up because it took nearly two years for her application to be accepted.

"I talked to her last week for 45 minutes," said Kelly Pickerel, 25, a friend in Culpeper. "She was totally happy. She was finally happy. She had bought a town house-condo. She was on a high with what she was doing. She loved it. She was terrified and excited at the same time."

"Robin was involved in everything," recalled William Pearson, principal of the Culpeper County High School. "She was just a very active, very energetic individual -- willing to help with anything, whether it was covering a class, chaperoning a dance or whatever. She was always willing to go, always willing to pitch in and help."

Ahrens, who grew up in Hudson, Wis., was one of six children. A family member who did not wish to be identified said Ahrens had gone to Hudson Senior High School, had worked on the ski patrol at Afton Alps near her home, and had been a six-year counselor at Camp Widji Wagan, a canoe camp in Ely, Minn.

A 1974 graduate of Utah State University, Ahrens had taught school in Firth, Idaho, near Pocatello, before moving to Culpeper with her then-husband, Charles Carter, who worked there, friends said. She also received a media specialist degree from James Madison University, according to the FBI.

Friends said Ahrens decided to leave teaching after her marriage broke up, and chose the FBI because she wanted adventure, a challenge -- as well as the chance to make a contribution.

"I think the driving thing with the FBI job was to keep the bad away from the good," Pickerel said. "For her whole life, she had done things for other people. This was the one thing she wanted to do for herself."

Ahrens was finally accepted into the training program in October. "I got this call," Pickerel said, "and I just heard Robin scream into the phone. And we both just started crying and jumping up and down."

Although Ahrens was supposed to finish the approximately three-month training course in January, she wrenched her back and had to stay in bed for several weeks. "She was very apprehensive about her back, but she just wouldn't give up," Pickerel said. "This was something she had decided to do."

Ahrens graduated from the FBI Academy at Quantico June 28, and threw a party for her family and friends. The next week, friends say, she left for Phoenix. Jennifer Campbell, who had known Ahrens since her days at Camp Widji Wagan, drove west with her.