Cardinal Camillo Ruini, Benedict XVI's vicar for Rome, made the announcement Saturday in a letter published in the diocesan weekly RomaSette.
The cardinal extended a public invitation to the ceremony April 2, the Monday of Holy Week, which will take place at midday in the Basilica of St. John Lateran.
The solemn opening of the diocesan phase took place June 28, 2005, less than three months after John Paul II's death.
In an interview with the Italian newspaper Il Corriere della Sera, Cardinal Stanislaw Dziwisz, archbishop of Krakow, and John Paul II's former secretary, said: "Now the word passes to the Curia in Rome."
After the closing of the diocesan investigation, the Roman phase will begin with the elaboration of a report to be prepared by a collaborator of the postulator of the cause, Monsignor Slawomir Oder, under the guidance of a relator of the Congregation for Saints' Causes.
That congregation will also receive the documents relating to the miracles attributed to John Paul II's intercession.
Monsignor Oder revealed Saturday that the investigation is concentrating especially on the case of a French nun who was cured inexplicably of Parkinson's disease.
Cardinal Dziwisz, who was John Paul II's assistant for 40 years, said: "Juridically, the beatification allows for only one ... devotion of a local character, namely, in the Diocese of Krakow. In this, perhaps, there is a contradiction, as he has surmounted all the barriers, he belongs to the whole world."
The cardinal continued: "It is certainly possible to 'make the leap' to beatification and begin immediately with the process to make him a saint. However, this depends on the Holy Father.
"For a long time, the process of beatification did not exist; there was only canonization. Beatification is a juridical rule. The Holy Father can decide otherwise."
"Canonization is very different from the theological point of view," added Cardinal Dziwisz. "The declaration of holiness is only a prerogative of the Pope; in this regard, the Holy Father cannot be substituted by any one, as that declaration is connected to infallibility."