American trauma experts said yesterday that the immediate danger posed by Pope John Paul II's gunshot wounds, and his chances of developing serious complications after surgery, depend upon which organs in his abdomen were damaged by bullets.

Following the pope's 4 1/2-hour emergency operation yesterday evening, a hospital spokesman said doctors had removed nearly two inches of the lower intestine, apparently referring to the large intestine or colon.

Trauma experts said wounds of the large intestine are considered far more serious than wounds of the small intestine, because they pose the risk of a life-threatening infection called peritonitis.

"It is . . . a graver danger to hit the colon [large intestine] as opposed to the small bowel," said Dr. Joseph M. Giordano, head of the trauma team at George Washington University Hospital and one of the surgeons who operated on President Reagan. He said this is because bacteria-loaded feces contained in the large intestine can leak out from a wound to contaminate the abdominal cavity, creating the potential for severe infection.

Although not every patient with a gunshot wound of the large intestine develops peritonitis, particularly if promptly treated with surgery and antibiotics, "it's a very significant possibility," said Dr. Philip Militello, deputy chief surgeon of the Maryland Institute for Emergency Services. "If the colon is injured by a bullet, we know that patient is going to get very, very sick. . . ."

He said that surgeons usually treat wounds of the large intestine by performing a colostomy, an operation in which a portion of the large intestine is brought outside the body so that waste material can be drained into a bag rather than traveling through the bowel to the rectum. This is often only a temporary arrangement, done so that feces will not contaminate the healing wound in the bowel.

Bullet wounds of the small intestine area a far less serious problem. Giordano said the hole created by a bullet in this area can often simply be sewn shut, or a small segment of the intestine can be removed -- like a section of rubber hose -- and the cut ends stitched back together. A patient who had only injuries of the small intestine "would ordinarily be in the hospital a week and then home," he said.

Giordano said anyone shot in the abdomen usually needs exploratory surgery immediately.He said it is necessary to operate because the abdominal cavity is so packed with vital organs that "the likelihood of hitting something, even if only bowel, is very high."

In cases like the pope's, as soon as surgeons open the abdomen, they first look for sources of hemorrhage, and control bleeding by clamping or tying off injured blood vessels, Giordano said. Fatal shock, caused by rapid bleeding, is the most immediate life-threatening consequence of an abdominal wound.

Reports soon after the shooting yesterday said that the pope was bleeding profusely, and hospital officials later said that he received transfusions of type A, Rh-negative blood.

Giordano said that after controlling bleeding, surgeons carefully check all the organs in the abdomen -- including the stomach, small intestines, large intestines, pancreas, spleen, liver, bladder and kidneys -- for injuries.

Injuries of some organs are much more dangerous than others. One of the major concerns was that a bullet might have hit the pope's pancreas, the organ located in the back of the upper abdomen when manufactures chemical enzymes that digest food.

A wound in the pancreas "is like taking a can of Adolf's meat tenderizer and pouring it in" the abdominal cavity, said Militello. He said enzymes that leak out of the pancreas can "dissolve all the tissues" surrounding the organ, causing inflammation and severe illness.

Giordano said injuries to the liver can also be serious, because they can cause massive bleeding and because the liver, like the pancreas, is an organ necessary for life.