Alexander Nikitin, a retired Russian naval captain, was acquitted today by a St. Petersburg court of espionage charges brought because he disclosed nuclear safety hazards aboard Russian submarines to a Norwegian environmental group.

The decision, nearly four years after Nikitin was arrested and after a second trial, was hailed as a major victory for environmentalists here, who have been under intense pressure from Russian security services not to probe the military's handling of nuclear materials.

The Nikitin case had attracted widespread attention in part because it centered on the dangers of one of the world's most concentrated zones of radioactive material, the waste and spent fuel from Russia's Northern Fleet submarines. Nikitin maintained that he had not committed a crime by bringing the dangers to public attention.

Nikitin co-authored two chapters of a 1995 report by the Norwegian environmental group Bellona that attempted to point to the dangers of radioactive waste from the fleet.

Nikitin's case also drew attention because he was accused under secret military orders that were adopted only after his arrest. Today's verdict appeared to strike down those orders; Judge Sergei Golets said their use was "a direct violation of the constitution."

"We are discussing the period August to September 1995," he said. "Later it became possible to apply new legislative acts, but not at that time."

The St. Petersburg prosecutor's office said it would appeal. However, a spokesman for the Federal Security Service, the successor to the Soviet KGB that investigated Nikitin, said the decision "is a ruling that we regard as having been reached on the basis of the law."

Nikitin was tried in the same court last year, but the case was returned to investigating authorities because the judge said the indictment was too vague. The security service issued a new indictment--the eighth in the case--but it was also classified as secret.

Today, Golets threw out the charges, saying they did not amount to a crime, and lifted an order that restricted Nikitin's travel outside of St. Petersburg.

"Despite what happened, what is happening and what may yet happen," Nikitin said in closing remarks to the judge, "I do not regret anything. I do not doubt even for a minute that it was the right choice."

Nikitin said that information about 30-year-old nuclear accidents or aging reactors could not have harmed Russia's defense capabilities, and that making the information public could help prevent accidents.

After Nikitin was arrested, the security services began investigating other people who had disclosed information about the navy's handling of nuclear waste. Grigory Pasko, a military journalist in the Far East port of Vladivostok, was sentenced in July to three years in prison for passing details of nuclear waste dumping to Japanese television, but the sentence was lifted immediately.