A paramedic on his way home from work early yesterday morning pulled an unconscious Great Falls teen-ager from the Potomac River after her car plunged down an embankment along the George Washington Parkway.

Karen Tansey, 16, who was on her way to the Madeira School in Greenway where she is a junior, was in critical condition last night with severe head and internal injuries at the Washington Hospital Center's MedSTAR Unit, a spokesman there said.

U.S. Park Police credited Wade Smith, 29, of Sterling, Va., who works as a MedSTAR paramedic, with saving the girl from drowning.

"It wasn't beyond the call of duty," Smith said in a telephone interview.

Park police said Tansey, who lives at 9329 Georgetown Pike, was going north along the parkway about 7:30 a.m. when she apparently lost control of the 1980 BMW she was driving. Her father, John T. Tansey, said yesterday that his daughter was en route from a family home in Georgetown to school.

Witnesses to the accident which occurred one-quarter mile north of Spout Run Parkway said it appeared that one of the tires blew out just before the car left the parkway.

The car crashed through a stone retaining wall and toppled 50 yards down an embankment, park police said. Tansey was apparently thrown through the windshield after the car rolled over several times before it came to rest at the water's edge, police said witnesses told them.

Smith, who was on his way home after a 12-hour shift with the MedSTAR Unit's helicopter rescue team, said he stopped with other motorists at the scene of the accident minutes after it occurred and began searching for possible victims.

Smith said the engine of the victim's car was still smoking when he ran toward it. Smith said he scanned the river bank for four to five minutes before spotting Tansey floating face down in about four feet of water directly in front of the vehicle. The car initially obstructed the view of the victim, he explained.

Leaning up against a tree, Smith said he reached into the water, pulled the girl by the back of her sweater up into his arms and administered mouth-to-mouth resuscitation.

"She was unconscious and not breathing and her face was blue," Smith said. "At first I thought she was dead." She began breathing on her own within seconds but did not regain consciousness, Smith said.

Two unidentified off-duty U.S. Capitol Police officers assisted Smith in attending the victim until an Arlington rescue squad arrived, police said. One of those officers radioed for help and the teen-ager was taken by helicopter to the MedSTAR unit.

Smith said yesterday he had been involved in rescuing people stranded in boats or on islands but had never pulled a drowning victim from the water.

Smith said he was unsure how much time elapsed before official rescue workers arrived. "I really don't know. I just had no track of time," he said.

Washington Post staff writer Michael Martinez also contributed to this story.