Pope John Paul II returned to his suite in a Rome hospital today for tests to determine the cause of a persistent fever that is slowing his recovery from gunshot wounds suffered in a May 13 assassination attempt, the Vatican announced.

The pope, 61, appeared pale and tired as he was readmitted to Rome's Gremelli Hospital, according to reporters who saw him. But he pulled himself up briefly in the back seat of his black convertible limousine, blessing a group of well-wishers before walking into the hospital on his own, they added.

A Vatican statement issued by the Rev.Romeo Panciroli said, "In the last few days, a persistent feverish movement has been registered in the pope's temperature that has altered the regular postoperative development, rendering slower and less satisfactory the recovery of his strength. This has led the doctors treating the pope to propose some diagnositical examinations that must be carried out within a hospital."

The hospital's chief medical officer, Dr. Emilio Tresalti, said the pope's life is not in danger. But he refused to describe his condition beyond the Vatican statement or reveal how high the fever is. Tresalti said the fever could come from an infection, as reported by an Italian magazine, but Vatican spokesmen said additional details on the pontiff's health would be announced only after hospital tests.

Panciroli, the chief Vatican spokesman, also refused to characterize the pope's condition with precision, saying only that it "raises the normal concern for a person who is under medical care to ascertain the cause of a fever." He added that the pontiff checked into the same 10th-floor suite where he recovered from the attempt on his life and that his six-man medical team -- the same that treated him during his first stay -- has no plans to put him in the intensive care unit.

Italy's most popular weekly magazine, Christian Family, appeared on the newsstands earlier today with an article saying the pope is suffering from a lung infection caused by returning too soon to his papal duties.

After being severely wounded in the assassination attempt in St. Peter's Square, the pope made what appeared to be a rapid recovery and -- reportedly against the advice of some of his doctors -- he was released from the hospital only three weeks later, on June 3.

He had been widely expected to rest at his summer residence at Castel Gandolfo 13 miles south of Rome in the Alban Hills. Instead, he returned to work. According to the Christian Family article, it was overexertion that caused what the magazine has referred to as "pulmonary complications with fever."

The magazine said that the pope tried to do too much by appearing at an ecumenical assembly in Saint Peter's Basilica on Pentecost Sunday only four days after his release from the hospital and by an eight-minute appearance afterward at his window to bless tourists and pilgrims in the square below.

The result, it said, was pulmonary complications with fever that developed the following week. His doctors advised a slowdown in activites. But this has not stopped him from brief appearances at his window every Sunday since then.

The pope's doctors issued a statement Tuesday denying press reports that the pope's appetite was poor and that vomiting and weight loss had forced him to resume a hospital diet. The statement said John Paul was gaining weight and "was eating regularly without any digestive problems."

The doctors also said they have not yet decided when to perform an operation that the pope must have to reverse the emergency intestinal bypass, or colostomy, performed on him after the shooting.

Christian Family, however, said one of the pope's doctors declared the pontiff is not yet strong enough to undergo the second operation. "Although not yet perfect, on the whole his health is good. However, I feel we must wait a bit longer. At present it is unthinkable that he should again be subjected to general anesthesia," the unidentified doctor was reported to have said.

Vatican sources had said earlier that they thought the operation would be performed early in July.

According to Panciroli, doctors began discussing the possibility of readmitting the pope to the hospital early yesterday, but a final decision was made only this morning. He also said the pope made a recording of the Angelus prayer and a brief message that will be played over loudspeakers in Saint Peter's Square at noon Sunday.

The man charged with trying to assassinate John Paul, Mehmet Ali Agca, remains in an Italian jail awaiting trial. Police are trying to trace the movements of Agca, 23, a Turk convicted of murder in his homeland, and to determine if he was helped by others.