VATICAN CITY – Excommunication. “Grave penalties” meted out by the pope himself.

The severest of punishments await anyone who breaks the sacred oath of secrecy during a conclave, the ritual filled process of electing a new pope that starts April 18.

Pope John Paul II set out the penalties in a 1996 document “Universi Dominici Gregis,” or “Shepherd of the Lord’s Whole Flock,” giving the cardinals who will choose his successor a set of detailed guidelines to ensure the centuries-old process of electing a pope is safe in an age of leaks to the press and cell phones.

In it, he called for a clean sweep by “trustworthy” technicians of the Sistine Chapel and adjoining rooms to prevent bugs and other audiovisual equipment from being installed. He banned telephones.

But with 3,500 accredited journalists roaming Vatican City and a world desperate to learn of the cardinals’ deliberations, many are wondering if news of a new pope will get out before the white smoke leaves the Sistine Chapel’s chimney.

“They’ve assured us there are ways to block all communications and conversations,” Chicago Cardinal Francis George told reporters Wednesday. “They’re taking precautions to prevent outside interference. … No cell phones, no laptops, nothing.”

Indeed, John Paul’s guidelines call for a near-monastic existence for the 116 cardinals who will vote in the conclave: no newspapers, magazines, radio, or TV. For the duration of the vote, they can’t communicate with anyone – in person, by phone, or letter – who hasn’t been vetted by the Vatican and taken an oath of secrecy.

“Should any infraction whatsoever of this norm occur and be discovered, those responsible should know that they will be subject to grave penalties according to the judgment of the future pope,” the document says.

Excommunication is one option, particularly for the handful of people who aren’t cardinals and will have access to the red-hatted “princes of the church.” They include regular priests who hear confessions, two medical doctors on call in case of emergency, and staff who will serve meals and clean up after the cardinals.

Bob Baer, a former CIA operative, said he found the idea of high-tech listening devices or transmitters that could eavesdrop on papal proceedings implausible.

“The only way you could record it is with a miniature recorder or cell phone,” he said. “It’s unlikely you’d ever get a listening post for a transmitter, or hope to get good reception.”

Despite such measures taken to ensure secrecy, John Paul changed the rules to allow the cardinals greater freedom while the conclave is under way.

Previously, cardinals were literally locked up “con chiave,” or “with a key,” inside the Apostolic Palace, its windows sealed, until they found a new leader of the Roman Catholic Church.

“It was easier because who was in, was in,” Archbishop Piero Marini, papal master of ceremonies, told reporters this week.

But John Paul, a veteran of two conclaves, decided to let the cardinals out, declaring that all of Vatican City was “con chiave.” Cardinals this time around will be housed in the $20 million hotel-residence Domus Sanctae Marthae and be allowed to use Vatican City chapels for Masses.

“The physical inviolability of the traditional conclave has been suppressed,” Archbishop Marini said.

The reasons for the change are practical: There was no running water in the makeshift rooms the cardinals used in the Apostolic Palace, and there was only one bathroom for every five or six electors, he said.

The new rooms in Sanctae Marthae, he said, were “discrete and simple but more comfortable.”

John Paul made clear, though, that the norms for secrecy must remain: “Provision shall be made to ensure that no one approaches the cardinal electors while they are being transported from the Domus Sanctae Marthae to the Apostolic Vatican Palace,” the document says.

That means no personal secretaries or communications directors who are juggling the cardinals’ many press appearances can pull their bosses aside once the conclave begins.

“We are expecting we’ll have no contact with them until we see white smoke,” said Susan Gibbs, a spokeswoman for Washington Cardinal Theodore McCarrick. “I think we can trust cardinals to take the oath of secrecy seriously.”