Artificial heart recipient Barney B. Clark dangled his legs over the side of his hospital bed yesterday and kicked them for 5 minutes at a time in his intensive care room at the University of Utah Medical Center, the hospital staff reported yesterday.

"I'd really like to stand up and stretch, but I just don't think I can make it yet," Clark told doctors after an early workout, hospital officials said.

University Vice President Dr. Chase Peterson said that Clark continued to make progress after two operations and was listed as "serious but stable." Nurses again called him an enthusiastic and cooperative patient with an excellent sense of humor.

Clark, 61, received the world's first permanent artificial heart last Thursday morning and underwent minor surgery Saturday night to seal a leakage of air from his lungs. Peterson said that chest drainage tubes were removed yesterday, signifying good recovery from the second operation, and no further signs of air leaks.

Clark's vital signs remain in the normal range, he said.

The artificial heart implanted in his chest is powered by an external unit riding on a "grocery cart" weighing more than 375 pounds. He will remain tethered to the cumbersome equipment for life, with his mobility largely limited to his home.

But within two years future recipients may receive a mobile nine-pound pack that would allow him to "stand in a grocery line and no one would know he had an artificial heart," said Steve Nielsen of the artificial heart laboratory. He said a portable unit, which could run for about 10 hours before repowering, has been tested on animals for up to two weeks.

Larry Hastings, who is in charge of monitoring the equipment driving Clark's heart, said yesterday that it has performed "extremely well."

According to spokesman Pam Fogel, Clark has indicated that he does not feel the heart "clicking or pumping" inside.

For the time being, Clark's exercise consists of dangling his feet over the side of the bed. Yesterday, nurses reported that when they tried to assist him in moving his legs he helped by attempting to bicycle them.

Doctors still hope to have Clark standing within in few days and "restore him to a general feeling of robustness," Peterson said.

Jane Stetich, one of Clark's nurses, pointed out at a news briefing the major differences between Clark and other heart surgery patients. Fogel said that in some ways it was easier to nurse Clark because he had no heart arrhythmias -- dangerous flutterings -- to worry about and was not taking the numerous cardiac drugs that are often prescribed after surgery.

Nurses said they want Clark to get more sleep after the disruption of the last several days, but Linda Giannelli, head nurse of the surgical intensive care unit, reported that he had recently been "sleeping and snoring a lot."

While resting he has been listening to a tape of Handel's "Messiah" by the Mormon Tabernacle Choir. Clark's wife, Una Loy, brought it to the hospital yesterday for her husband to listen to as he recuperated. The retired Seattle dentist and his family are members of the Mormon church.

Hospital spokesmen said that Clark was still sipping apple juice and water and had not yet asked for solid food.

While his progress is encouraging, they emphasize that he is not out of the woods. Doctors continue to watch for signs of infection, the greatest worry, and hope that if all goes well he might go home in a few weeks.

Clark has already lived longer on the artificial heart than two earlier patients who received artificial hearts as a temporary measure while Texas surgeon Denton Cooley waited for human heart transplants.

Doctors at the University of Utah say that they do not plan to begin considering a second mechanical heart implant in the immediate future because they do not want to shortchange Clark's care in any way.