ROME (Reuters) - Less than a month after Pope John Paul died, millions of mourning Italians will get to see a portrayal of the late pontiff next week in a television film dedicated to his early years.

"Karol, The Man Who Became Pope" portrays Karol Wojtyla from his days as a university student in Krakow during the invasion of Poland by Nazi Germany in 1939, through his vocation to the priesthood and on to his surprise election as pope in 1978.

The producers are already working on a sequel dedicated to his years as pontiff and due to go into production in September. Both will be aired on a private channel controlled by Italian Prime Minister Silvio Berlusconi's Mediaset group.

The young Wojtyla, who initially saw his future in the theater, is played by Polish actor Piotr Adamczyk, who made no secret of the difficulty of the task.

"It was a mixture of joy, happiness and this heavy feeling of responsibility," Adamczyk told a news conference after a screening near the Vatican on Thursday.

"To understand what Pope means to us Poles you have to know how Poland changed during his pontificate.

"To try to depict this kind of personality, you can imagine the challenge. It would be a challenge for any actor, especially a Pole...to prepare the spirituality, the mysticism and the charisma." Director Giacomo Battiato said although it was not a documentary, the dialogue included many words and phrases used by the future head of the Roman Catholic Church in his writings.

The film's producer, Pietro Valsecchi, recalled the moment in which Pope John Paul II was informed during an audience of the planned film.

"He gave me a very ironic look -- and in that look I saw the phrase, 'Don't get it wrong in the film,"' Valsecchi said. "It made me determined to make sure I didn't."

The film, which is being marketed internationally, will be shown in two parts beginning on Monday April 18 -- the day when cardinals gather at the Sistine Chapel to begin the election of Pope John Paul's successor.