WHEN THE WORLD gave its first serious sizing-up of Pope John XXIII -- seeing him as a geniune spiritual visionary and not merely a round and jolly storyteller -- he was a sick man on his way to being a dying man. This was in October 1962 when he opened the Second Vatican Council and called it a "new Pentecost."

The first session of the council ran only 60 days. Those two months were enough for Pope John to stir new energies of reform within the Church and excite new surges of respect from without. At his death from inoperable cancer at 81 in June 1963, he had fulfilled his personal goal, as set out in his will: "I was born poor, I have always been poor, and I want to die poor."

From Peter Hebblethwaite's carefully crafted and reflective biography, the poverty of Angelo Roncalli -- 58 years a priest, five a pope -- is seen to be the classic detachment of all simple spirits: outer wealth meant nothing, inner wealth meant everything.

Hebblethwaite, 54, is a British journalist living in Oxford, England. Since 1979 as the Vatican affairs writer for the National Catholic Reporter, he has been the only Vaticanologist -- of whom there are few in the first place -- regularly filing copy to American readers. Hebblethwaite is one of the many journalistic reasons for the consistent excellence of the National Catholic Reporter and its way of getting to issues that the large news organizations miss or think unimportant.

Like a side chapel off the main altar, Pope John's story includes Hebblethwaite's reportorial details about the Vatican's Curia before and during the five-year papacy. It seems that Roncalli had an ecumenical approach to religion long before he welcomed Protestants, Moslems, Buddhists and other observers to Vatican II. In 1936, as the apostolic delegate to Istanbul and archbishop to the city's 35,000 Catholics, Roncalli began using Turkish in worship services. This was when Latin -- and Latin only -- had been the Church's language. The future pope wrote in his diary: "When the Tanre Mubarek Olsun (Blessed Be God) was recited, many people left the church displeased . . . (But) I am happy. On Sunday the Gospel in Turkish before the French ambassador; today the Litany in Turkish before the Italian ambassador. The Catholic Church respects everyone. The Apostolic Delegate is a bishop for all and intends to honor the Gospel which does not admit national monopolies, is not fossilized, and looks to the future."

Hebblethwaite adds the details: "Roncalli saw his linguistic innovations (in Istanbul) as a way of making the Church more genuinely 'Catholic.' He was denounced to Rome. In his October 1936 retreat he remarks that 'the difference between my way of seeing situations on the spot and certain ways of judging things in Rome hurts me considerably; it is my only real cross.'"

DIFFERENCES with Rome would bedevil Roncalli even when he was the bishop of Rome and pope. On October 11, 1962, he opened Vatican II with a speech. Hebblethwaite compared the Latin transcript provided by Vatican radio with the later translation in Acta Apostolicae Sedis, the official collection of papal documents as kept by the Curia bureaucracy. The latter edited out several lines of progressive thought. "When the pope discovered these outrageous changes in late November 1962," Hebblethwaite writes, "he was too canny to sack the editor of Acta Apostolicae Sedis. He simply quoted himself, in the original non-edited version, in important speeches."

So the saints, too, know how to get even, and, in Pope John's case, doubtlessly enjoyed a laugh doing it.

Hebblethwaite, who worked seven years on this project, is a reliable analyst of John's temperament. He recounts an interview with Msgr. Loris Capovilla, the pope's secretary. John loved a saying of St. Bernard: "See everything, overlook much and improve a little." (Omnia videre, multa dissimulare et pauca corrigere). Capovilla explained that John's practice of this philosophy was "not a sign of weakness or compromise; it involves rather a precise knowledge of situations and the ability to overcome obstacles gradually." Hebblethwaite concludes with justification, "In other words, 'Good Pope John' was nobody's fool and knew exactly what was being muttered behind his back. He saw it all (omnia videre). The signal . . . to the Roman Curia was clear: John would not be pushed around or manipulated by anyone. He was his own man."

Not always. Sometimes he was too much the Italian man. Blood was thicker than holy water when in 1939 he said that Mussolini is "guided to act for the good of Italy" and that the Church should "be grateful" to Il Duce. As late as April 1939, Roncalli was saying "I don't believe we will have a war."

When war did come, Roncalli, in Istanbul, worked to rescue Jews. With Turkey still being neutral in 1943, Istanbul was the only escape route for Jews fleeing Nazi Europe and hoping to make it to Palestine. Documents are cited by Hebblethwaite to support the claim that Roncalli did all that was possible to intervene on behalf of Jews. He helped save thousands. Years later -- in 1960 at the Vatican -- an American rabbi led a delegation of 130 Jews to meet with John. The Pope greeted them, "I am your brother."

One of the pleasures in reading this well- written biography that covers 81 years is that companion works are available, beginning with Pope John's Journal of a Soul. The story told there -- of personal growth, of the interior development of compassion and faith -- is reinforced by Hebblethwaite's account of how those virtues flourished despite church politics and unchurched politicians. If the Vatican needs a miracle to bring on John's canonization, there it is.