VATICAN CITY — Pope Benedict XVI installed his first group of cardinals yesterday, crowning 15 new princes of the Roman Catholic Church with scarlet hats symbolizing their willingness to shed blood in defense of the faith.

Nearly a year after he became leader of the world's most powerful religious institution, Benedict used a solemn, regal ceremony in St. Peter's Square to urge his followers to proclaim a message of love "far and wide" that would unite and bolster Christians everywhere.

The new cardinals, who join an elite club that will one day choose Benedict's successor, included Hong Kong's Joseph Zen, an outspoken critic of China's human-rights record and repression of Christians. During the ceremony, a prayer was read in Chinese honoring "all those who still suffer for their Christian faith."

The group also included Americans William J. Levada, who was previously selected by the incoming pope as head of the Vatican body that enforces doctrine and thus became the most powerful American at the Holy See. As head of the San Francisco region, he had overseen the Diocese of Honolulu.

Another notable: As archbishop of Boston, white-bearded Franciscan Sean O'Malley has had the job of repairing damage in sex-abuse scandals that forced the resignation of his predecessor, Cardinal Bernard Law.

Selecting cardinals is one of the most important tasks for a pope, and the roster of new choices is always scrutinized for insight into the direction a pontiff plans to take the church, or for political or doctrinal messages. Because it was former Cardinal Joseph Ratzinger's first time installing cardinals since his election to succeed the late Pope John Paul II, the event, known as a consistory, attracted special attention.

Also significant was Benedict's decision to hold what one church official called a brainstorming session with all cardinals on the eve of the consistory. Several senior prelates have called for a more "collegial" church hierarchy that consults its members more regularly.

As church bells pealed under cloudy skies, the newly designated cardinals paraded into crowded St. Peter's Square, smiling broadly and waving to supporters. They were bareheaded and each was dressed in a bright-red cassock with a similarly hued mozetta, or cape.

Benedict, wearing papal white and a fur-trimmed red-and-gold cape, called each man's name in Latin. One by one, they went before him, knelt and received Benedict's blessing. The pope then placed on each man's head a red biretta, a four-cornered satin hat emblematic of his new station.

Levada, a close ally of the pope's, went first. He kissed Benedict's hand, and then the pope rose unexpectedly, placed his hands on Levada's shoulders and kissed each cheek.

Levada said that he faced the day "with a heart full of emotional gratitude and trepidation."

Another poignant moment came when Stanislaw Dziwisz, the archbishop of Krakow, Poland, and longtime personal secretary to John Paul, received his hat. Both Benedict and Dziwisz were visibly moved as they embraced on a stage that the Polish prelate had shared for so many years with the late pontiff.