Italian police have launched an internation manhunt hunt for a second Turkish suspect they believe was working with the assailant of Pope John Paul II, who today celebrated his 61st birthday by moving from the intensive care unit to a private suite of the General hospital.

Interior Ministry Under Secretary Angelo Sanza said in an interview that the police were "almost certain now" that there was second person involved in last Wednesday's shooting of the pontiff, who suffered three gunshot wounds in St. Peter's Square. He identified the second suspect as Mehmet Sener.

Sener has been described in Italian press reports as the mastermind behind the 1979 slaying of a Turkish newspaper editor who was gunned down by Mehmet Ali Agca. Agca is being held here for the attempted assassination of the pope.

The Interior Ministry official said Sener had been spotted in the piazza shortly before the shooting and identified by unnamed witness on the basis of a picture provided to the Italian police by Turkish authorities.

At one point, however, he backed off slightly, saying it was "probably" Sener who was the second 100 to 200 yards away from Agca and leaving the piazza on a motorbike.

Another Turkisk right-wing extremist described by Italian national television as a "probable accomplice" of Agca, Oral Gelik, also is being sought here and in other Westerm European natons. It was not clear what role police suspect Gelik of playing in the attempt on the pope's life or whether they believe he was in St. Peter's Square at the time.

While Sanza's declaration seemed to lend weight to the growing conviction in some circles that there was a conspiracy against the pope's life and that a terrorist organization was behind it, the country's antiterrorist police chief took a more conservative approach. Alfredo Lazzerini told The Associated Press that Agca "may not have been. As for an international conspiracy, it's a very remote possibility."

Yesterday, Italian Interior Minister Virginio Rognoni traveled to Bonn for talks with his West German counterpart Gerhart Baum, regarding the continuing interrogation of Agca, who Turkish authorities insist stayed for some time in West Germany.

On Wednesday, Five Western European countries sharing information on terrorist activities will hold a special meeting of their top security officials here for the same purpose. They are Italy, France, Switzerland, West Germany and Austria.

Agca, whose intensive interrogation resumed today after a short respite yesterday, continues to insist he acted alone, without help or guidance from any organization or person.

Italian sources familiar with the results of the first 72 hours of interrogation said the 23-year-old Turkish terrorist was providing extremely detailed answers on matters of relatively little importance and then avoiding similar replies to key questions.

"He is very clever," said one source. "On important matters, he says he doesn't remember."

Italian magistrates in charge of Agca's interrogation have obtained a second film shot by a tourist of the entire sequence of actions leading up to the shooting of the pope.

The film is said to have been taken only a few feet away from the open white in which the pontiff was standing as he circled the piazza. It is reported to show Agca holding the gun in both hands above his head, similar to a picture already appearing in newspapers around the world, and firing the weapon twice at a distance of seven to eight yards from the pope.

It appears to confirm Agca's contention that he was the only one involved in the actual shooting, the Milan newspaper Corriere della Sera reported today. But, it added, the film still does not exclude the possibility that Agca belonged to a terrorist organization that was extremely dangerous "because of its branches and ties."

The usually cautious, staid Corriere ran a banner headline Friday saying "international plot," although hard evidence for this is still lacking.

Meanwhile, thousands of get-well and birthday cards from around the world arrived at the hospital today for the convalescing pope, whose recovery was reported to be continuing its "favorable evolution" despite the persistence of a slight fever.

The pope celebrated his 61st birthday by moving into a suite on the 11th floor of the hospital equipped with all the medical machinery necessary to monitor his condition as well as with a portrait of the Black Madonna of Czestochowa, who is regarded by Catholic Poles as their country's special patron saint.

Dr. Emilio Tresalti, the hospital's chief medical officer, told reporters there was still "some concern" about the pope's fever and a continuing danger of infection to the part of his intestines badly damaged by a 9 mm slug that passed through his abdomen.

Apparently reflecting his continuing concern, five international doctors, including two Americans, have been invited to come to Rome to act as consultants to the Italian physicians in charge of treating him. Their names were not released.

[In Buffalo, N.. it was reported that Ann Odre, the 58-year-old widow wounded by the same gunman who shot the pope, has suffered a slight setback in her recovery in a Rome hospital. In an interview with the Buffalo Evening News her daughter, Joanne Kenjarski, reportedly said, "She's not doing as well as she was on Saturday." Kenjarski said her mother's color was not as good and she had more pain today than over the weekend.]