Pope Benedict XVI has taken the extraordinary step of ordering an investigation into a conservative Roman Catholic order that recently disclosed that its late founder had fathered a child.

The Vatican secretary of state, Cardinal Tarcisio Bertone, said investigators would visit all of the institutions run by the Legionaries of Christ, one of the fastest-growing orders in the Roman Catholic church.

Bertone said in a letter to the head of the order posted Tuesday on the Legion's Web site that the Vatican was stepping in "so that with truth and transparency, in a climate of fraternal and constructive dialogue, you will overcome the present difficulties."

The Legionaries of Christ was much admired by the late Pope John Paul II for its conservative view, strict loyalty to Vatican teaching and success in enrolling recruits. However, its Mexican founder, the Rev. Marcial Maciel, was long dogged by allegations he sexually abused seminarians.

In 2006, a year into Benedict's pontificate, the Vatican disciplined him on the sexual abuse charges, asking that he lead a "reserved life of prayer and penance," and refrain from celebrating Mass in public. Maciel died in 2008 at age 87.

Last month, there were fresh revelations about Maciel's sexual life. The Legionaries' head, the Rev. Alvaro Corcuera, has not publicly provided details, but individual Legion leaders have confirmed that Maciel had a relationship with a woman and fathered a daughter who is now in her 20s and living in Spain.

While the abuse charges had long cast a cloud over Maciel, the latest disclosures tarnished the Legion's reputation even more. Observers have questioned how it can carry on since the order is so closely affiliated with Maciel's persona.

Maciel is held up as a hero whose life is to be emulated; seminarians and members of its lay affiliate study Maciel's writings and they pray that the spirit of the founder lives on in their behavior.

Corcuera said the Legionaries welcomed the Vatican investigation "with deep gratitude," saying Benedict was offering his support as the order faces "our present vicissitudes related to the grave facts in our father founder's life."

The Vatican spokesman, the Rev. Federico Lombardi, said the investigation was the way the Vatican can get firsthand information about a problem in the church. In a similar move in 2004, the Vatican sent a team of investigators to an Austrian seminary following revelations that seminarians were hoarding child porn.

More recently, the Vatican sent teams of investigators to visit all 229 U.S. seminaries following the church abuse scandal.

The team of prelates for the Legionaries investigation will be named by the Vatican and will get under way over the next several months, Lombardi and Corcuera said.

Founded in 1941 in Mexico City, the Legion says it has more than 800 priests and 2,500 seminarians worldwide. Its lay branch, Regnum Chrsti, says it has 50,000 members globally. In the U.S. alone, the Legion has a couple of dozen prep schools and has been building a college — the University of Sacramento — in California.

Pressure had been building in recent weeks for an external review of the Legion, even among some of the group's staunchest defenders, to see if any of its current leaders had covered up Maciel's wrongdoing and to make sure no further misdeeds were taking place.

Baltimore Archbishop Edwin O'Brien traveled to Rome in February to question Legion leaders about Maciel's misdeeds, and upon return warned his parishioners not to join the Legion or Regnum Christi.

"He was asked to do penance in 2006 and still they were holding him up as their hero, their icon," O'Brien said in a recent interview with The Associated Press. "That shows how insensitive they were and I think, right now, unaware of the damage that's being done not coming out and saying things."

Although the Legion has made no official statement about the outstanding abuse claims against Maciel, some Legion leaders say the latest revelations about Maciel fathering a child gives credence to the abuse allegations.

"There was some validity to those as well," said the Rev. Thomas Williams, a moral theologian who has held leadership positions for the Legion in Rome.

"It's really come as a very hard blow to all of us. This is a very very big deal," Williams said in a recent interview with EWTN, the Catholic TV network.

Genevieve Kineke, a former Regnum Christi member who now presses the movement to end its secrecy, said the church leaders in charge of the evaluation will have to overcome what she called the "culture of solidarity" inside the order.