A 26-year-old man yesterday became the third person in as many weeks to be injured in falls in the Montgomery County portion of the C&O Canal National Historical Park, according to the National Park Service. All three men survived.

"We're a little surprised at the number of falling accidents we're having all at one time," said National Park Service Ranger Michael Brown. "People have been cooped up in their houses all winter and they're dying to get out, and just taking chances they wouldn't normally take," he said.

Brown said the park normally averages about three serious fall-related rescues a year.

In yesterday's incident, Michael Lancaster, of 4301 Jones Bridge Rd., Bethesda, was midway up Billy Goat Trail near Sandy Landing shortly before 2 p.m. when he lost his footing and fell, according to the Montgomery Fire and Rescue Service. Lancaster bounced off some rocks and landed in the Potomac River near the shore, they said. He was able to swim to the shore, where he collapsed.

Brown said a person on the other side of the river saw Lancaster fall and alerted bystanders, who covered the man with heavy clothing until rescuers from the park service, Montgomery County and the U.S. Park Police arrived.

Lancaster was flown by helicopter to Washington Hospital Center where he was treated for hypothermia, bruises and lacerations. He was listed in fair condition last night, according to a hospital official.

Lancaster had no safety or survival equipment and was not wearing hiking shoes, Brown said. The ranger described Billy Goat Trail, named for its "extremely rough terrain," as one of the toughest trails in the park to hike.

An 18-year-old youth climbing with his father was injured two weeks ago on the west end of the trail when he fell about 35 feet after a new rope they had knotted slipped. Both climbers were novices, Brown said. It took 12 men three hours to pass the litter carrying the youth over the trail, he said. Yesterday, park service rescuers were able to use a boat to move Lancaster to the U.S. Park Police helicopter area.

Last week, a teen-ager fell about a dozen feet while climbing on Olmsted Island.

The ranger attributed many accidents at the park to carelessness and inexperience. The park, portions of which are in the District and several Maryland counties, drew 4 1/2 million visitors last year, a 10 percent increase over the year before, he said.

"The big problem here is that most people in this area are very urbanized," Brown added. "They don't realize . . . this area . . . can kill them."

After yesterday's fall, he said, Lancaster noted " 'Nothing is as easy as it looks.' "