LOS ANGELES, SEPT. 15 -- Pope John Paul II ventured into the world's entertainment capital on a day when the Los Angeles Times' lead feature story explored the life of "The Last of the Blonde Bombshells -- Saga of Ex-Sex Kitten," and he urged industry leaders today to be forces for "great good" rather than promoters of "dehumanized" and "casual" sex, greed and violence.

"All the media of popular culture which you represent can build or destroy, uplift or cast down," the pope told a select audience of entertainers and media personalities ranging from Bob Hope and Charlton Heston to Norman Lear and Oliver Stone. "It is the difference between death and life . . . . And it is a matter of choice."

John Paul II, a playwright and poet who worked in the underground Polish theater during World War II, has used global communications to great effect during his nine years as pope, in a sense bringing the Vatican into the media age.

Traveling today through Hollywood to Universal Studios on the sixth day of a 10-day U.S. tour, he paid homage -- and issued stern warnings -- to what he called "one of the most important American influences on the world today."

The ballroom of the Registry Hotel was full of dark, elegantly tailored suits and flossy party dresses. Agents bragged to clients about the number of tickets they were able to cadge for the speech. Producer Merv Griffin and Jack Valenti, head of the Motion Picture Association of America Inc., entered the room together.

"If we had to get rid of greed," Griffin joked, "I'd have to cancel 'Wheel of Fortune' and 'Jeopardy.' "

"If we got rid of greed," Valenti said, "there wouldn't be any projects in this town."

Talk show host Phil Donahue came arm-in-arm with his wife, actress Marlo Thomas, who said she wished the pope "would embrace women in the church and be a little more humane about homosexuals and listen to people like Father McNulty." McNulty addressed the pope in Miami at the start of his tour, describing the joys and concerns of America's dwindling number of priests.

To the newspaper and broadcast journalism leaders in today's audience, the pope said that the Roman Catholic Church recognizes the need for freedom of speech and freedom of the press but that those rights "imply corresponding duties" -- an obligation to truth and completeness and a willingness to listen as well as inform.

"There is always the danger of communication becoming exclusively one-way, depriving audiences of the opportunity to participate in the process," the pope said, adding later: "You must seek to communicate with people, not just speak to them."

The pope has made the responsibility of sharing and acting on truth -- God's truth, the church's truth -- a central theme of his peregrination through the American South and West. He told the assembled communicators that they must not abuse their protected position under the First Amendment.

"Precisely because your responsibility is so great and your accountability to the community is not easily rendered juridically, society relies so much on your good will," he said. "In a sense the world is at your mercy. Errors in judgment, mistakes in evaluating the propriety and justice of what is transmitted and wrong criteria in art can offend and wound consciences and human dignity."

The pope observed that the communications industry, with its "fast pace of news and changing tastes" and vast sums of money, has created special problems for those who practice it.

"Do not let money be your sole concern, for it is capable of enslaving your art," he said, adding that the industry "places you under extreme pressure to be successful, without telling you what 'success' really is. Working constantly with images, you face the temptation of seeing them as reality. Seeking to satisfy the dreams of millions, you can become lost in a world of fantasy."

The pope's two-day visit to Los Angeles, with its 2.6 million Roman Catholics, began with an eight-mile parade this morning that took the popemobile past large, colorful crowds in Hispanic neighborhoods, Koreatown, Chinatown and Little Tokyo. The motorcade ended at the 117-year-old St. Vibiana's Cathedral.

Speaking before 1,000 dignitaries -- including Gov. George Deukmejian and Mayor Tom Bradley -- and other worshipers, the pope spoke of the difficulties Catholics face in exercising their faith in a secular society and thus being "out of step with majority opinion."

An unscheduled exchange there appeared to delight the pope. As he concluded his remarks with "God bless Los Angeles," a woman's voice rang out from the rear of the cathedral: "God bless you, Holy Father."

When the nervous laughter and applause died down, he reclaimed the microphone and said, "I thank you for this blessing . . . . It is true that the pope in a special way needs the blessing of the people of God."

Later, he met with 6,000 young people gathered in the Universal Studios auditorium and linked via satellite to similar gatherings in Denver, Portland and St. Louis. He dealt with the increased incidence of teen-age suicides in the United States, urging the youngsters to keep their faith and thus their hope.

"Why does it sometimes happen that a seemingly healthy person, successful in the eyes of the world, takes an overdose of sleeping pills and commits suicide?" the pope asked. "Why on the other hand do we see a seriously disabled person filled with great zest for life? Is it not because of hope?"

In the evening, he celebrated Mass for an estimated 100,000 worshipers at the Los Angeles Coliseum, arriving in a helicopter that bypassed massive traffic jams.

In his homily, John Paul renewed his theme of fidelity to Christian teachings as the antidote to contemporary problems -- and he seemed to appreciate California's reputation as a state so contemporary that trends -- and problems -- often appear here first.

"Today, the people of California play a major role in shaping the culture of the United States, which has such a profound influence on the rest of the world," he said. "Your state also leads in research and technology designed to improve the quality of human life and to transcend the limitations which impede human freedom and progress."

But "no amount of economic, scientific or social progress can eradicate our vulnerability to sin and to death," he said. "Technology . . . increases what we can do, but it cannot teach us the right thing to do."

The Mass here created some controversy when the Los Angeles archdiocese ruled out women as assistants during Holy Communion because, a church spokesman said, "enough priests and deacons are available."

Specially trained lay men and women are permitted to assist in the distribution of the consecrated communion elements when there are not enough priests. In San Antonio Sunday, Texas bishops allowed women to take part in the papal Mass because many men were unavailable for rehearsals, a spokesman there said.