The testimony by the editor, Alan Rusbridger, gave a public airing to the debate over how to balance press freedom against national security concerns, an issue that became more acute once The Guardian began publishing material leaked by Mr. Snowden in June.
The American and British governments have said the disclosures, which detail how the National Security Agency and its equivalent in Britain, Government Communication Headquarters, gather vast amounts of data, damage national security and help hostile governments. Journalists and transparency advocates have countered that the leak spurred a vital debate on privacy and the role of spy agencies in the Internet age.
Mr. Rusbridger said Tuesday that the governments’ measures “include prior restraint,” as well as visits by officials to his office, the enforced destruction of Guardian computer disks with power tools and repeated calls from lawmakers “asking police to prosecute” The Guardian for disclosing the classified material in news articles.
As he testified before a Parliamentary committee on national security, he faced aggressive questioning from lawmakers, particularly those of the ruling Conservative Party. Some asserted that The Guardian had handled the material irresponsibly, putting it at risk of interception by hostile governments and others. Others said the paper had jeopardized national security.
At one point during the hearing, Mr. Rusbridger was asked, to his evident surprise, whether he loved his country. He answered yes, noting that he valued its democracy and free press. After Mr. Rusbridger’s testimony, a senior British police officer, Cressida Dick, refused to rule out prosecutions as part of an investigation into the matter.
Since the revelations, newspapers, particularly those that have dealt with Mr. Snowden’s material, have also had to adjust to a harsh new reporting environment, security experts and journalists said, as governments and others seek secret material held by reporters.
“The old model was kind of like your house,” said Marc Frons, the chief information officer of The New York Times. “You locked your front door and windows, but not your desk drawer, even if it had your passport inside. In the new model, you have locks on everything.”
The Guardian, The Washington Post and The Wall Street Journal declined to comment about internal security arrangements.
But Mr. Rusbridger told Parliament that the newspaper “went to more precautions over this material than any other story we have ever handled.”
Senior Guardian editors were initially skeptical this year when asked to hand over their cellphones before discussing Mr. Snowden’s documents, said a person with knowledge of the reporting process, who did not want to be named discussing confidential security procedures.
That soon changed when they reviewed the information Mr. Snowden had supplied, this person said. The documents, they came to realize, would be of intense interest not only to the American and British governments, from which they were taken, but also to other governments like China and Russia seeking an espionage edge and hackers seeking to embarrass either government agencies or the publications reporting on the material.
Eventually the same editors insisted that meetings be held in rooms without windows and that any electronic devices nearby be unplugged. Computers that contained the information could never be connected to the Internet. And reporters who needed to consult with colleagues in other countries about the documents had to fly them over physically and meet in person, despite the extra costs. On one occasion, Mr. Rusbridger said, encrypted documents were sent via FedEx.