By Philip Pullella

VATICAN CITY (Reuters) - Jozef Wesolowski, a former archbishop and papal ambassador to the Dominican Republic, will stand trial on criminal charges of paying for sex with minors and possessing child pornography, the Vatican said on Monday.

The trial, due to start on July 11, will be the first on such charges inside the tiny city-state that is the headquarters of the 1.2 billion-member Roman Catholic Church.

Vatican sources said the decision by the president of the Vatican's tribunal to indict Wesolowski could not have been taken without a green light from Pope Francis. They said it was another sign of the pontiff's intention to get tough on sex abuse by clergy.

Wesolowski's trial will be the highest profile judicial event in the Vatican since Paolo Gabriele, a former papal butler, was convicted in 2012 of stealing and leaking private papers of former Pope Benedict XVI. He was convicted and later pardoned by Benedict.

The 66-year-old former Polish archbishop, who was "apostolic nuncio", or Vatican ambassador, in Santo Domingo for five years, was arrested last September and detained in the Vatican. It was the first arrest there related to paedophilia charges.

"The announcement of Wesolowski's trial, while welcome, is minimal, belated and expected," said Anne Barrett-Doyle of BishopAccountability.org, an independent research group that helps tackle the issue in the Catholic Church.

"It remains to be seen whether the Vatican City State will administer real justice (or if holding the trial in the Vatican) was effectively a way to protect the church from the damaging revelations that likely would occur if the former archbishop had been tried in the Dominican Republic or Poland," she said.

Wesolowski was recalled to Rome by the Vatican in 2013 when he was still a diplomat in Santo Domingo and was relieved of his duties after Dominican media accused him of paying boys to perform sexual acts. The reports led to a police investigation.

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"DELICATE PROCEDURE"

The former archbishop would dress in layman's clothes, including a baseball cap, and frequent a beach front area known as a venue for poor child prostitutes, according to the local media that broke the story.

After his recall to Rome, he was defrocked by a Vatican tribunal and lost his diplomatic immunity. The pope ordered a criminal investigation.

After his arrest, Vatican inspectors found child pornographic material on his computer.

The Vatican's statement said the trial would be "a detailed and delicate procedure".

If convicted, Wesolowski is unlikely to spend time in the Vatican's jail, which consists of just a few rooms attached to its courthouse.

He would likely be sent to an Italian prison as part of an international agreement between Italy and the Vatican, or be extradited to the Dominican Republic or his native Poland, Vatican officials have said.

(Editing by Gareth Jones)