A rookie Virginia state trooper sped through Arlington County and into Georgetown yesterday morning where he scaled a 12-foot chain-link fence and jumped into the cold Potomac River to rescue a woman who had survived a plunge from Key Bridge minutes earlier.

When Trooper Perry Freeman pulled the woman, who later gave authorities two different names, from the river at 2 a.m., she was suffering from what doctors said later was exposure and a wrist fracture. The woman, who told officials she was 29 years old, was treated at George Washington University Hospital and released.

It is rare that people who fall or jump from area bridges survive, said D.C. Harbor Police Officer John Fitzgerald. Last year, Harbor Police recovered 22 bodies from beneath bridges, including four who are believed to have jumped the 61 feet into the Potomac from Key Bridge, which links Georgetown with Rosslyn.

"It's more the exception that they live," said Fitzgerald. "They're very lucky." Police gave no official explanation for the woman's fall.

Freeman, 24, who moved from his native Chesapeake, Va., to Springfield in February after he graduated from the state police academy, said luck also played a part in the woman's rescue yesterday. Freeman said he had never been in Georgetown until Wednesday night.

While patrolling I-66 in North Arlington early yesterday, Freeman and another trooper were dispatched to the Key Bridge to respond to reports that a woman had jumped near the bridge's highest eastern arch. When he arrived, Freeman said, he found Trooper Cindy K. Robbins shouting to a woman who was swimming from the center of the river toward the Georgetown shore.

"I decided we weren't doing any good standing there on the bridge talking to her because that wasn't going to get her out of the water," Freeman said. He jumped back in his cruiser and, with lights flashing and siren screaming, crossed the bridge to M Street and turned right on Wisconsin Avenue and parked in a fenced-in area between the river and K Street.

While Robbins shined a high-powered flashlight on Freeman from the bridge above, he squeezed through a gate on the lot, climbed over a 10-foot fence topped with two feet of barbed wire, and ran 75 yards downriver along rocky terrain to the woman. He found a 15-foot drop from the shore, Freeman said.

By then, the sight of police cars racing through Georgetown streets had attracted a crowd. "Someone produced a 50-foot rope and I used that to climb down the embankment," Freeman said. The rope was held by a group of onlookers. As Freeman tried to grab the woman, he said, but she began swimming away from him, upriver toward the bridge.

So Freeman jumped "about rib-deep into the water . . . it was extremely cold . . . and brought her back to where the rope was and tied it around her and told them the citizens to pull. I had to bring her back because the rope wouldn't stretch over to where she was going . . . . When I looked up, the fire and rescue people were there."

Freeman, who lost his tie during the rescue, said the woman was distraught when she was hauled from the river. "She was crying and very emotionally upset," he said. "She said she was sorry . . . . She was very lucky."