Egyptian President Anwar Sadat said today that the cancer-stricken, deposed shah of Iran is in "very serious condition" after being readmitted to a Cairo military hospital.

Sadat, who is in Alexandria, said he had received an urgent message from the hospital saying that the condition of the deposed shah, Mohammad Reza Pahlavi -- who had returned to the hospital suddenly last night -- has worsened, the official Middle East News Agency reported.

"We should all pray for him," Sadat said. Asked by reporters whether the shah's death is imminent, Sadat replied: "Only God knows that, and I wouldn't want to hear of such a thing."

Sadat said he was receiving hourly reports on Pahlavi's condition and planned to go to Cairo to see him if there is no improvement.

A presidential spokesman said later that Sadat would return to the capital Sunday, interrupting his stay in Alexandria that had been expected to last until mid-July. The spokesman declined to say if Sadat would go to the Maadi military hospital, where the former Iranian ruler is being treated. t

Other sources, however, indicated that the president is expected to visit Pahlavi Sunday.

Officials at the hospital in a Cairo suburb refused to discuss the deposed monarch's condition with reporters, and further details of his medical situation were unavailable.

Dr. Abdel Hamid Khalil, who examined the former ruler today, told a radio interviewer only: "As the president said, the shah is truly in serious condition."

Dr, Nabil Fawzi, a radiologist, said, "The complications which have set in resulted from the basic disease which afflicted the shah for years." This was a reference to the lymphatic cancer for which Pahlavi originally sought treatment.

Sadat disclosed on June 17 that Pahlavi, 60, had suffered a relapse, attributed to complications resulting from chemotherapy for treatment of cancer, which doctors said had spread to his liver. Sadat said today that Pahlavi also contracted pneumonia at about that time.

There was no confirmation today of reports late yesterday that Pahlavi had contracted either typhoid or paratyphoid.

French and Egyptian doctors reportedly were treating him here.

The return of Pahlavi to Iran, which considers him a criminal, has been the principal demand of Iranian militants in exchange for the release of 53 American hostages held since last Nov. 4.

Pahlavi fled his homeland at the height of the anti-shah revolution in January 1979, stopping first in Egypt before traveling on and eventually settling in Mexico. His admission to a New York hospital last October led to seizure of the Americans in Iran. In March, at Sadat's invitation, Pahlavi flew to Cairo from Panama for the spleen-removal operation.

Photographs taken of him in May showed him to be in better health than he was two months earlier. He said in an interview with The Washington Post on May 23 that he was feeling better and regaining lost weight.

The ousted ruler's personal physician, Houston surgeon Michael DeBakey, was reported to be in Europe today on a long-planned visit. A spokesman for DeBakey in Texas said he did not believe the physician planned to go

Pahlavi's offical spokesman, Robert Armao of New York, as at the hospital, but was unavailable for comment.

Secrecy has shrouded Pahlavi's condition during most of his exile in Egypt. He, his wife and their three children have been staying as guests of Sadat at Kubbeh Palace, usually reserved for visiting heads of state.

Sadat last visited Pahlavi June 11. The Egyptian president has been meeting with aides in Alexandria to plan for this week's meetings in Washington about possible resumption of Palestinian autonomy talks with Israel.