Edward Snowden has secured his highest endorsement yet in the US when former vice-president Al Gore described the leaking of top secret intelligence documents as "an important service".

Asked if he regarded Snowden as a traitor or whistleblower, Gore veered away from the "traitor" label. He refused to go as far as labelling him a whistleblower but signalled he viewed him as being closer to that category than a traitor, saying: "What he revealed in the course of violating important laws included violations of the US constitution that were way more serious than the crimes he committed."

Snowden, the former CIA and National Security Agency computer specialist, leaked US and British documents to the Guardian and Washington Post in June last year, starting a worldwide debate on the balance between surveillance and privacy. His revelations have led to proposed changes in legislation in the US and a backlash against government surveillance by major telecoms and internet companies.

But he remains a polarising figure in the US. An NBC poll a fortnight ago showed 24% backing him and 34% disagreeing with his actions, with 40% having no opinion. Among the younger generation there was more support, with 32% backing him and only 20% opposed, with 47% having no opinion. Some members of Congress have welcomed the revelations but refuse to go as far as supporting Snowden, who is wanted by the US and has sought asylum in Russia.

Gore, interviewed at the Southland technology conference in Nashville, Tennessee, was asked if he viewed him as a whistleblower or a traitor. "I hear this question all the time. I'm like most people: I don't put him in either one of those categories. But I'll be candid and give you want you want. If you set up a spectrum. "

The interviewer interrupted: "How would you define it?"

Gore replied: "I would push it more away from the traitor side. And I will tell you why. He clearly violated the law so you can't say OK, what he did is all right. It's not. But what he revealed in the course of violating important laws included violations of the US constitution that were way more serious than the crimes he committed.

"In the course of violating important law, he also provided an important service. OK. Because we did need to know how far this has gone."

The documents released by Snowden showed massive government surveillance but also the extent of co-operation between the government and the large telecoms and internet companies.

Gore called on the internet companies to work with the public to help draw up a "digital Magna Carta" that provides protection of freedoms. "They need to pay attention to correcting some of these gross abuses of individual privacy that are ongoing in the business sphere," he said.

Snowden's hope of a return to the US is dependent on a change in a major shift in opinion that would allow him to escape a lengthy prison sentence. His supporters will seize on Gore's comments to help make the case that he is a whistleblower and should be allowed to return to the US as a free man. Ben Wizner, Snowden's US-based lawyer, said: "Al Gore is quite obviously right. Regrettably, the laws under which Snowden is being charged make no allowance for the value of the information he disclosed. Whether the NSA's activities violated the law or the constitution would be irrelevant in a trial under the Espionage Act."