Dead or alive, no liberal theologian seems safe from the increasingly visible heresy-hunters in the Vatican. In mid-March, L'Osservatore Romano, the official Vatican newspaper, attacked the ideas of Karl Rahner. A year before his death in 1984, Rahner, a German Jesuit and a universally revered theologian, coauthored "The Unity of Churches -- A Real Possibility." The Vatican said the book contained "grave errors" and "unorthodoxy."

A few days later in a more publicized case, the Rev. Leonardo Boff, a Franciscan theologian who has worked among the poor of Brazil, had his teachings condemned by the Vatican. Boff's ideas on liberation theology are said to be a danger to the faith.

Vaticanologists say every papacy has a theme. Pope John Paul II has taken church authority as his chosen mission. Under him, the dead Rahner and the living Boff are only the latest to feel the authoritarian power of Rome. Religious orders that encouraged such priests as Robert Drinan, Miguel D'Escoto and Ernesto Cardenal to work in politics were overruled by the Vatican. In countries like the United States and Ireland, where Rome believes the faithful have been led astray by overly frisky theologians, conservative bishops have been installed.

In the midst of all this, the memory of a different kind of pope and leadership has been freshened. A major biography, "Pope John XXIII: Shepherd to the Modern World," by Peter Hebblethwaite, is being published this month. Although Pope John's brief years of service (1958-1963) were only a walk-on in the 20 centuries of Christianity, their warmth contrasts stunningly with the tensions now coming from Rome. Much of what Boff and Rahner wrote in recent years is traceable to the thinking of Pope John.

The Second Vatican Council, which John opened in 1962, was a welcome break with the centuries-old tradition of condemning errors. Today, said John, the church "prefers to use the medicine of mercy rather than severity. She considers that she meets the needs of the present age by showing the validity of her teaching rather than by condemnations." Hebblethwaite, a British writer, says Pope John acted "with great tact and skill. He did not deny that errors existed in the contemporary world; indeed, they positively abounded. In a characteristic image he said that 'errors often vanish as swiftly as they arise, like mist before the sun.' "

It shouldn't be so, but this was the approach of a religious revolutionary. It put John into a combat zone against entrenched conservatives in the Vatican who saw the new pope as politically naive and theologically loose. In the style of religion that believes in condemnations of others and pronouncements of perfection for itself, John XXIII was a threat. He was redirecting the church to its Biblical pre-Western origins, when it was merciful, poor and pacifistic. With Christianity simplified to its essence, John saw no need for a constant display of an I'm-right-and-you're-wrong kind of authority.

In "Pacem in Terris," Pope John's enduring peace encyclical, a seed of thought was planted that later blossomed in the liberation theology of Latin America. This is the approach that applies parts of Marxist economic analysis to eliminating poverty. The encyclical holds that "good and commendable elements" can be found in systems of thought that also contain falsity. Liberation theologians say the same. Pope John had other shocking views. He said once that "the Russian people are a wonderful people. We must not condemn them because we don't like their political system . . . We can talk with them. We must always try to speak to the goodness that is in people."

John welcomed Protestants, Buddhists and Muslims to Vatican II. Twenty years before, as an archibishop in Istanbul, he introduced the native language -- Turkish -- in worship services, not Latin. The Hebblethwaite biography provides the bleak details of sniping cardinals and Curia underlings categorizing all this as grave error and unorthodoxy. Their mentality is back in favor.

Pope John's breadth and openmindedness is not to be found in the Vatican of today. Later this year, a synod of bishops is scheduled to meet in Rome to examine, among other things, the changes brought on by Vatican II. During his papacy, John was not safe from the church's authoritarians. His reforms may not be safe either.