Pope John Paul I, a frequent newspaper contributor who once wanted to be a journalist, gently admonished reporters in a special audience yesterday to "focus on the heart and substance of our ministry and not the incidental details."

His eyes twinkling behind steel-rimmed glasses, the pope said he read with some amusement the speculation on papal candidates in news reports preceding his surprise election by the College of Cardinals last Saturday.

He likened the journalistic speculators to the Italian editor who covered the France-Prussian war "not by concentrating on the important discussions between Napoleon III and the King of Prussia but by dwelling on whether they smoked cigarettes and whether they wore red or beige pants."

"I know people are interested in these deails," the pope said as the audience hall ecohed with laughter and the applause of more than 1,000 journalists "But I hope that during my pontificate you will not only report the incidental details but also the heart of the story of the church."

Italian experts, meanwhile, joined the Vatican's own security squads in preparing for the pope's inaugragation today by drawing up massive antiterrorist measures and checking the vast square in front of St. Peter's Basilica for possible snipers' nests and danger spots.

Security officials refused to discuss the precautions they were taking but said an "army" of about 7,000 agents and sharpshooters was being mobilized from Italy's police and armed forces and the Vatican's own corps to preserve order.

Italian police said they were particularly concerned over protest demonstrations planned by leftist groups against some of the inauguration's more controversial guests.