NEW YORK – Christians who mostly turned the other cheek as “The Da Vinci Code” climbed the best-seller list are launching a counteroffensive now that Dan Brown’s novel is set to hit the big screen.

As the movie’s May 19 opening draws nearer, Roman Catholic and other Christian leaders are unveiling new Web sites, taking out full-page ads to “debunk” the work’s claims and speaking out in the media and from the pulpit.

Even during Holy Week, the upcoming film was on the minds of prominent clerics worldwide.

The archbishop of Canterbury, the Most Rev. Rowan Williams, denounced the book’s controversial premise that Jesus married Mary Magdalene and had children, calling it “the stuff of imagination.”

“It’s almost that we’d prefer to believe something like this instead of the prosaic reality,” Williams, head of the worldwide Anglican Church, said on Easter Sunday.

In a Good Friday sermon at the Vatican, the Rev. Raniero Cantalamessa, Pope Benedict’s personal priest, was more blunt. “Christ is still being sold for 30 pieces of silver … this time to publishers and filmmakers,” he said.

The reclusive author, Dan Brown, denies his writing is anti-Christian. “This book is not anti-anything. It’s a novel,” he writes on his Web site. “I wrote this story in an effort to explore certain aspects of Christian history that interest me. The vast majority of devout Christians understand this fact and consider “The Da Vinci Code’ an entertaining story that promotes spiritual discussion and debate.”

Pat Ryan Garcia, a spokeswoman for the U.S. Conference of Catholic Bishops, said the organization has sought to provide “proper Catholic answers” to questions the book raised for the faithful. But she said the conference decided to “ramp up its efforts” when the first movie trailer for “The Da Vinci Code” declared: “Seek the truth.”

“He wants to play both sides of it,” Garcia said of Brown. Though the author stresses the book is fiction, she noted he also presents readers with a “fact sheet.”

During the Lenten season in March, the conference created a Web site called “Jesus Decoded,” hoping to refute aspects of the book. It also produced an hour-long documentary of the same title on the life of Jesus.

Many of the new Web sites offer a point-by-point challenge to Brown’s “fact sheet” and other aspects of his storyline.

As successful as the book has been – more than 40 million copies have been sold worldwide – Garcia said the movie will be even more of a “media phenomenon” because it stars Tom Hanks, is directed by Ron Howard and will have a single worldwide release. “A lot more people go to the movies than read books,” she said.

Among other Christian responses to the upcoming film:

-A leading evangelical Protestant seminary, the Westminster Theological Seminary in Philadelphia, debuted a rebuttal site on Good Friday. The site seeks to “create doubt about doubt,” a seminary spokeswoman said.

-The Church Communication Network is planning a May 21 satellite broadcast to 3,000 Protestant churches nationwide featuring a discussion of the movie by three Christian authors.

-James Dobson, a leading evangelical and founder of the conservative advocacy group Focus on the Family, will deliver two radio broadcasts on “The Da Vinci Code,” set for May 1 and 2.

-Even the usually secretive Roman Catholic sect Opus Dei, which is featured negatively in the book, released a video Wednesday to show how founder St. Josemaria and Opus Dei “have had a positive effect on the lives of thousands of people,” a spokeswoman for the group said.