ROME — Pope John Paul II is receiving added nutrition through a tube in his nose, the Vatican announced yesterday, acknowledging for the first time that the pontiff's recovery from throat surgery has been slow.

The pope, who is breathing through a tube in his throat, was fitted with the feeding tube after widespread reports that he has been having difficulty swallowing food.

The announcement came two hours after the pope made another brief appearance at the window of his apartment, during which he struggled, but failed, to speak to pilgrims gathered in St. Peter's Square for his regular weekly audience.

The Vatican didn't say when the tube was inserted, but there was no sign of it during his four-minute appearance at the study window. Medical experts said a nasal feeding tube, which would typically remain in place between meals, would have been visible had it been present.

This latest twist to the saga of the pope's health problems brought closer the possibility that the Vatican may one day have to grapple with the dilemmas posed by a permanently incapacitated pontiff. Although the Vatican said the pope, 84, spoke before he left the hospital March 13, he has not spoken publicly since.

The Vatican portrayed the tube's insertion as another step toward his recuperation from the tracheostomy performed two weeks ago to alleviate breathing difficulties he experienced after coming down with influenza. "To improve the calorie intake and encourage a complete recovery of strength, feeding has begun through the positioning of a nasal gastric probe," said the statement issued by the pope's spokesman, Joaquin Navarro Valls.

The communiqué was less upbeat than previous ones, and for the first time the Vatican used the word "slow" in reference to the pope's recuperation.

The nasal feeding tube is a less invasive procedure than the one used in the abdominal application and is usually intended to be temporary. A plastic tube is inserted through the nose, down the esophagus and into the stomach, enabling processed food to be delivered directly to the stomach, medical experts said.

Whether the pope will recover his ability to eat normally will depend in part on the causes of his swallowing difficulties. If they are linked solely to his recent throat operation, the extra nourishment may help him recover his strength and aid the healing process.

But if his swallowing difficulties are caused by the muscle degeneration associated with Parkinson's disease, he may never be able to eat properly again, medical experts said.

If that is the case, it may soon become necessary to perform the more drastic procedure of inserting a tube directly into his stomach, because the nasal tube will, over time, cause ulceration and infection in the stomach and the esophagus, said Luisa Riccardi, a gastroenterologist.

Normally, a nasal tube can be left in place 7 to 10 days, after which it can be replaced if there are no complications. But in the case of weakened patients with muscle degeneration, such as the pope, a nasal feeding tube is often inserted as a prelude to the more drastic stomach operation, called a percutaneous endoscopic gastrostomy, she said.

Riccardi suspects doctors have prescribed a period of nasal feeding to help build the pope's strength in preparation for the stomach operation.

The stomach tube also wouldn't confine the pope to bed. But it is also, usually, irreversible.