* Court rules against admitting cardinals' evidence
* Former butler appears at trial, smiling but pale
* Gabriele often stared into space in 2 hour, 20-min hearing
* Security so tight reporters' own pens were not allowed in (Adds further details of hearing)
By Philip Pullella
VATICAN CITY, Sept 29 (Reuters) - Pope Benedict's butler, accused of using his access to the pope to steal papers that he thought would expose Vatican corruption, suffered a blow on Saturday's first day of his trial when judges refused to admit evidence from the Church's own investigation.
Gabriele's arrest in May, after police found confidential documents in his apartment inside the Vatican, not only threw a spotlight on allegations of malpractice but also pointed to a power struggle at the highest levels of the Church.
The 46-year-old Paolo Gabriele, an unassuming man who served the pope his meals and helped him dress, looked pale at his first public appearance since May. He smiled as he chatted with his lawyer but often staring into space during a hearing that lasted just under two and a half hours.
His lawyer, Cristiana Arru, had asked the court to allow as evidence the results of an inquiry by a commission of three cardinals who questioned Vatican employees, including prelates, about the leaks of the documents to Italian media.
But chief judge Giuseppe Dalla Torre, sitting before a crucifix and with a large, framed picture of Benedict looking down from the wall, said the commission answered only to the pope and had "no relevance" to the Vatican City's penal code.
According to an indictment issued in August, Gabriele told investigators he had acted because he saw "evil and corruption everywhere in the Church" and wanted to help root it out "because the pope was not sufficiently informed".
Domenico Giani, head of the Vatican police force, told the court that 82 boxes of evidence had been seized in Gabriele's apartments in the Vatican and in the papal summer residence.
Arru had wanted to see the commission's transcripts in the hope that they could help to explain her client's motives.
19TH CENTURY CODE
Instead, trial evidence will be based solely on the results of the investigation by a Vatican prosecutor and Vatican police.
The trial is being held under a 19th-century criminal code, so Gabriele did not enter a plea and did not speak. He is expected to testify when the trial resumes on Tuesday.
In a mostly procedural session, the court split off the case of Claudio Sciarpelletti, a Vatican computer expert charged with helping Gabriele who was not present in court.
The session was attended by eight police witnesses. The other four witnesses, including the pope's private secretary, Monsignor Georg Ganswein, were not present but are expected to give evidence next week. Gabriele's family also did not attend
Dalla Torre, wearing a black robe with gold epaulettes and a white, ruffled cravat, said he hoped to wind up the proceedings next week. It was not clear when the verdict would come.
The self-styled whistle-blower, who wore a smart light grey suit and light grey tie, could be jailed for four years.
Gabriele, who has said he saw himself as an "agent of the Holy Spirit", is widely expected to be found guilty because he has confessed.
"He has done harm by leaking this information because there will always be somebody who will take advantage of these things to denigrate the Church," said Rome resident Sergio Caldari in Saint Peter's Square.
Another local onlooker, Giovanni Maisto, said he was hopeful that the trial could mark "a new dimension of openness and transparency" in the Church's affairs.
Gabriele, a father of three who lived a simple but comfortable life in the city-state, told investigators after his arrest that he believed a shock "could be a healthy thing to bring the Church back on the right track".
MONTHS OF INTRIGUE
His capture capped nearly five months of intrigue and suspense after a string of documents and private letters found their way into the Italian media.
It was the latest embarrassment for a Church still reeling from the scandal of worldwide sexual abuse by members of its clergy.
The most notorious of the letters were written to the pope by Archbishop Carlo Maria Vigano, currently Vatican's ambassador to Washington, who was deputy governor of the Vatican City at the time.
In one, Vigano complains that when he took office in 2009, he discovered corruption, nepotism and cronyism linked to the awarding of contracts to outside companies at inflated prices.
Vigano later wrote to the pope about a smear campaign against him by other Vatican officials who were upset that he had taken drastic steps to clean up the purchasing procedures.
Despite begging not to be moved, Vigano was later transferred to Washington by Secretary of State Cardinal Tarcisio Bertone, effectively the Vatican's prime minister.
Since the papal state has no prison, Gabriele would serve time in an Italian jail, though the pope is widely expected to pardon him.
Television cameras, tape recorders and computers were not allowed into the court, a small, wood-panelled room with an ornate papal emblem on its ceiling.
The eight journalists allowed to cover the hearing were even blocked from bringing their own pens inside for fear that they could contain hidden recorders or cameras. (additional reporting by Gavin Jones and Eleanor Biles; Editing by Kevin Liffey)