By Mica Rosenberg

LEON, Mexico (Reuters) - Pope Benedict's first full day in Mexico was clouded by fresh allegations the Vatican hid evidence of sex abuse by one of the country's most prominent Roman Catholic leaders for decades.

The authors of a new book say a trove of once-secret Vatican documents prove Church officials ignored complaints of drug use and molestation of seminarians by the late Father Marcial Maciel, founder of the Catholic order the Legionaries of Christ.

Adding to the criticism of the Church, victims of abuse by priests in Mexico came forward to seek an audience with Benedict, but said their calls have not been answered. Church officials acknowledged in 2009, a year after Maciel's death at the age of 87, that the charismatic Mexican cleric had led a double life, secretly fathering children and lavishly spending the generous donations of his followers.

Now more than 200 leaked documents from confidential Church archives reveal a mass of new testimony against Maciel, says the book, "La voluntad de no saber" (The will not to know).

"The Vatican not only knew about Maciel's pathologies, but they tolerated them and protected him," said religion expert Bernardo Barranco, who wrote the book 's introduction.

Barranco presented the 255-page work on Saturday in the central city of Leon, while the 84-year-old pontiff was resting after his long flight from Italy.

Among the evidence is a 1979 letter to Church authorities from John McGann, the Bishop of Rockville Center, New York, that cites allegations by Legionnaire Juan Vaca, who said his years of sexual abuse by Maciel began when he was 13.

The Bishop told a Vatican official in the United States Vaca raised "serious questions concerning Father Maciel's stability" in written testimony given to Church officials. Another 1954 letter describes in detail Maciel injecting a form of morphine.

Despite years of allegations, Maciel - who had the support of the previous Pope John Paul - was spared official censure until 2006 when Benedict ordered him to retire to a life of "prayer and penitence."

VICTIMS REQUEST MEETING

Benedict has made a point of speaking with victims of abuse in a number of other countries includingMalta, the United States and Australia, but has no meeting scheduled in Mexico.

"We asked to see him and hoped he would sit down with us like he has done in other countries. The Church said no victim had reached out to them, which is just another lie to protect priests who are still active," said Jesus Romero, who says he was molested by a Catholic priest at the age of eleven.

Father Jorge Martinez from Mexico's Episcopal conference said it would be difficult for the pope change his official schedule but his message to children on Saturday afternoon would speak to the suffering of youngsters affected by violence.

The Legion, founded by Maciel when he was in his 20s, is a powerful order with many prominent members among Mexico's business leaders. Backers have included the owners of Mexican bread maker Bimbo and Carlos Slim, the world's richest man.

The order runs private Catholic schools and charitable organizations in 22 countries via its network of 800 priests and 2,600 seminarians. The order's lay movement, known as Regnum Christi, has around 75,000 members.

Benedict arrived on Friday afternoon to cheering crowds, and holds a Sunday mass where over 300,000 believers are expected. On Monday he travels to Cuba to conclude his first trip to Spanish-speaking Latin America in his seven years as pope.

(Additional reporting by Philip Pullella and Miguel Angel Gutierrez; editing by Todd Eastham)