A Washington teen-ager bitten in the shoulder by one of two deadly Gaboon vipers stolen from the National Zoo was removed from the critical list at Children's Hospital yesterday, but doctors remained guarded about his prognosis.

Louis (Junior) Morton, 16, was listed in serious condition in the hospital's intensive care unit. Doctors there voiced concern not only about nerve and tissue damage in the vicinity of his wound but about possible kidney failure as his body attempts to rid itself of the snake's highly toxic venom.

"His condition is improved," said hospital spokesman Harold Kranz Jr. "His bleeding has stopped and the (medical) team is now watching cautiously as the initial course of anti-toxin serum has been administered."

He said Morton "is being kept comfortable with pain killers" but would remain hospitalized at the very least "for many weeks."

Hospital spokesmen said doctors are working "with very little knowledge." The world's medical literature, they say, holds only 10 recorded cases of Gaboon viper bites, most of them in Africa where the massive, exotically patterned snake normally lives.

Hospital sources said doctors have used about 20 of an estimated 50 10-cc vials of antivenin flown in from zoos in New York, Philadelphia and Baltimore.

Morton was bitten shortly before midnight Monday while carrying the two thick-bodied, 4 1/2-foot snakes in a plastic garbage bag slung over his shoulder as he left a Metrobus at 15th and K streets NW. The bus driver said Morton had been carrying the bag when he boarded the bus near the zoo about 11:15 p.m.

Yesterday, neighbors near the Morton apartment at 1307 Savannah St. SE, said the boy is fond of snakes and other pets and that he had talked repeatedly over the weekend of plans to visit the zoo on Monday. Grace Barnes, a friend of the Morton family, said he spoke of bringing home an alligator.

Zoo officials said that in addition to the snake cages shattered Monday night, a plate glass window was broken in an outdoor enclosure housing several yacare caimans, small crocodiles from South America. None of the animals was taken, however.

Morton told a police officer he found the snakes in the bag in Rock Creek Park. No one has been charged in connection with the break-in at the zoo.

Meanwhile, zoo officials said the two Gaboon vipers, recovered near McPherson Square Monday night by police, including officer Ray Harper, an experienced snake handler, may die of the shock of the night's events.

Extremely sedentary creatures, unaccustomed to even slight movement in their environment, they were showered with glass from their broken cages, dragged from their enclosures and stuffed into the garbage bag, thrust into the cold air and dropped onto the pavement after one of them bit Morton through the bag.

"They were jostled, squeezed, and manhandled," said Laurie Bingaman, of the zoo's herpetology department. "That's the most activity these snakes will ever experience."

The cold alone could give them pneumonia or respiratory problems, Bingaman said, but in addition they apparently bit each other while in the bag. Though they are immune to their own venom, Bingaman said, the wounds could become infected.

Bingaman said the snakes' handlers will wait several months before offering the snakes their regular weekly ration of one dead rat each. "We'll let their systems calm down again," she said.

Even at that it may take a while to tell if the snakes are off their feed. The male, zoo officials say, normally eats only about once every three weeks.

The seriousness of a Gaboon viper's bite appears due to the extreme virulence of the venom--which attacks both the central nervous system and the body's ability to produce blood clotting agents--and the depth and amount of its injection. The viper's extraordinary fangs can grow in excess of 1 1/2 inches in length--nearly twice the length of most other venomous snakes.

R.L. Ditmars, in the book "Snakes of the World," reports that a person bitten on the index finger with just one fang lost consciousness after one hour despite an antivenin injection and excision of the wound. The arm quickly swelled, the hand grew dark blue and the finger turned black.

The symptoms were accompanied by cold sweating, bloody urine and extreme respiratory difficulties.

Blood transfusions, additional incisions and renewed antivenin injections and heart medications saved the patient's life. But he was bedridden for weeks.