President Carter fell and broke his left collarbone yesterday while skiing cross-country at his mountaintop retreat at Camp David, Md.

Flown by helicopter to Bethesda Naval Medical Center, Carter spent about an hour in the hospital, and returned to Camp David just before 5:30 p.m. At Bethesda, X-rays confirmed that the bone was broken near where it connects with the breastbone, and he was placed in a "figure-eight" harness to immobolize his shoulders. His left arm was placed in a sling.

"The president was in considerable pain," White House deputy secretary Rex. L. Granum said last night. "He was given some pain medication, and will probably require additional medication for the next day or two."

Carter was accompanied to and from the hospital by White House physician William M. Lukash and by Rosalynn Carter, with whom he had been skiing when he fell. Granum said one of Carter's skis caught on a rock as he skied down a hill behind the Aspen Lodge on the Camp David grounds.

Granum said there was about three inches of snow on the ground at Camp David when Carter, his wife, Lukash, White House Marine Corps aide John Kline and two Secret Service agents ventured out for their second cross-country skiing of the day.

Granum said Carter fell at about 3 p.m. a few hundred yards from the lodge and walked back to the lodge, where Lukash put a sling on his arm and a harness around both shoulders.

Carter, 56, is an avid skier, jogger, tennis and softball player. He still runs three to four miles fives times a week. A year ago September, he collapsed from near-exhaustion in a cross-country footrace near Camp David.

There was no immediate indication what effect the injury would have on the president's daily routine. Clearly, jogging, skiing or any other athletic activity is out of the question for the rest of his administration. Doctors say a broken collarbone takes weeks to mend. The arm in which the broken collarbone rests must be kept immobilized in a specially rigged sling the entire time.

"The injury is a fracture of the medial aspect of the left clavicle," Granum said last night. "This is the area closest to the sternum [breastbone]."

Granum said this was the second time that Carter had broken his left collarbone. He said he had broken it once before during a jujitsu match when he was a midshipman at the U.S. Naval Academy more than 35 years ago.

The president will be in the figure-eight harness for the next six to eight weeks, Granum said.

The harness is placed around the shoulders to bring both shoulders back together under the same strain. The sling keeps the arm immobilized, with the forearm flexed at a 45-degree angle and the palm of the hand resting on the opposite collarbone. The sling may come off sooner than the harness.

"The president is right-handed, so we don't expect he'll miss to much," Granum said. "He was shaking hands with the staff in the hospital, so I don't imagine he's too bad off."

In addition, the injury is sure to lighten the president's daily routine for the next four weeks at least. Clearly, jogging and skiing, his two favorite athletic pasttimes, are out of the question for awhile.

Granum said that Carter has no plans to alter his coming schedule, which includes a trip to the Sugar Bowl in New Orleans on New Year's Day. Until then, Granum said, the president will stay at Camp David.