In the eerie light of the Siberian night, a dozen Soviet soldiers, armed with rifles, sprang from a drab green military truck, kneeled on a sandy beach, and leveled their weapons at John Christopher Cook and four other anti-whaling protesters from the environmental group Greenpeace.

The soldiers spoke no English and the landing party--armed with anti-whaling leaflets and photographic gear--spoke no Russian.

"That's when I began to to think there could be some unfortunate developments," Cook said in an interview from Greenpeace's Seattle office yesterday. "I got concerned."

Cook and four companions were arrested 10 minutes after they landed last Monday.

A sixth was picked up by a helicopter as he tried to race a small boat back to the Greenpeace ship Rainbow Warrior, and a seventh was arrested after he took a radio ashore so Soviet officers could talk to an interpreter aboard the ship.

The seven--six Americans and one Canadian--were returned to the Rainbow Warrior late Friday at sea midway between Siberia and Alaska.

The publicity stemming from the Soviets' subsequent detention of the seven has served to increase international attention to the killing of whales for commercial purposes, an issue that the International Whaling Commission (IWC) addressed last Friday by slashing commercial hunting quotas more than 18 percent.

The protesters' Siberian invasion has also focused the international spotlight on Greenpeace and its administrative director, Cook, 30, a former Capitol Hill aide who joined Greenpeace two years ago.

Cook, somewhat dazed, following five days of often tense Soviet detention and an almost equally intense barrage of international media attention, said yesterday that he believes the Greepeace affair helped sway the IWC decision, and also publicized the issue beyond his organization's wildest hopes.

Despite the stress of the Soviet captivity, Cook said he and the group were so committed to their goal that they generally put aside their fears and concerns about their own fate.

"We went there in the firm belief that we were doing something decent, honorable and important," he said, "And when you have that on your side, you don't feel like you are in over your head."

The other Washington area resident in the Greenpeace group, 35-year old veteran environmentalist Nancy Foote, was still in Alaska yesterday. Her family has since talked with her by telephone from their southern Frederick County, Md., home. "She was excited but kind of in a fog from being tired," a sister, Elaine Foote, said yesterday.

In an interview from Seattle, Cook described the group's imprisonment by the Soviets as a series of long stretches of boredom punctuated by intense moments of anxiety, such as the instance when Soviet officials told the group they might face three years' imprisonment.

The Greenpeace activists were kept by the Soviets in a spartan barracks at an undisclosed location, Cook said. The windows were closed and papered-over, but the captives could see the silhouettes of the armed soldiers patrolling outside. The five men and two women were kept in separate quarters.

The food was plentiful, he said, with large portions of rice, wheat, fresh bread, and slabs of meat at every meal--which Cook said was not very welcome to the several vegetarians in the group.

"The accommodations were comfortable, but it was five of us in a 20-by-20 foot space. The breathing air quickly ran out, and we weren't allowed to open windows. We hadn't showered or changed our clothes in a week," Cook said, "It got a little bit stale in there."

The Soviets were initially puzzled about Greenpeace's motives and tactics, Cook said. Soviet authorities, he said, were led by a functionary who always wore wraparound sunglasses and was addressed by the group simply as "The Chief." Cook, who served as the official spokesman for the group, said "The Chief" told him through an interpreter that Soviet officialdom had not decided whether the intrusion was to be handled as an administrative matter or as a criminal act, punishable by three years imprisonment.

"The chief said if it was a criminal case, these nice beds and hearty meals will disappear quickly . . . and the interrogation will begin, and it will proceed, and will proceed, and will proceed . . .," Cook said.

"We willingly violated Soviet law and we were prepared to face the consequences," Cook said, "But the idea of three years in a Soviet prison seemed a little imbalanced against the nature of the violation."

Initially, the Greenpeace group had gone ashore in the Siberian fishing village of Lorino following a 15-hour voyage from Alaskan waters in Greenpeace's trawler, the Rainbow Warrior.

Secrecy was not a priority. Cook said the group had sent a telegram to Soviet Premier Yuri Andropov a week earlier telling Andropov that they would be arriving to protest the Soviets' refusal to abide by the IWC's decision to ban the killing of whales for commercial purposes by 1986. The USSR, Norway and Japan have refused to obey the ban.

The invasion was timed for maximum publicity purposes to coincide with the IWC meeting in Brighton, England. Cook said Greenpeace hoped to take to the IWC filmed proof that the Soviets were using whale meat to feed mink. IWC guidelines allow the killing of whales only for human consumption. Soviet officials at the IWC meeting disputed Greenpeace's contention that the film shows processing of whale meat to be used to feed mink.

Throughout the captivity that began with a strip-search, an interrogation and a medical exam, Cook said, the Greenpeace group was sealed off from the outside world. He said they were unaware whether the Soviets had captured the mother ship and whether Greenpeace had succeeded in getting the film and the international attention it sought.

Finally, on the fourth day, after a visit and extensive interviews with the senior judicial official in the eastern Siberian province, the verdict was rendered.

"The Chief walked into the room," Cook recalled, "He was in strict formal attire, in military garb with an outer dress coat. He came in and said: 'The senior judicial official has decided that your situation will be treated as an administrative matter.' "

"We didn't jump up and down and yell yahoo. But there was a real burden lifted from our shoulders."

The Greenpeace band was made to sign a statement acknowledging their violation of Soviet sovereign territory, Cook said. He said he wrote the confession, which all the group members signed, and he said he made sure that the statement reaffirmed Greenpeace's belief that its action was just.

"We tried to convey the idea to the Soviets that it was worth it, that there are people willing to compromise their own liberty for principle," Cook said. He said the group felt it important to try to educate the Soviets on the environmental issue, even in the context of the captivity.

"The whale is a special case," he said, "It is a magnificent species . . . with every right to exist in its own ecosphere. Beyond that, the whale is a symbol that represents pretty much the shortcomings of modern thought . . . that the planet's resources are dominated for short-term gain."

Cook, who graduated from the University of Kentucky in English literature and then worked on a family tobacco farm, said he learned to appreciate the environment from his family. He came to Washington a few years ago as an aide to Rep. Carroll Hubbard Jr. (D-Ky.) and became interested in the environmental group after meeting Greenpeace leaders at a party.

Late Saturday night, no sooner had Cook and the others been pulled aboard the Rainbow Warrior than they were descended upon by scores of journalists from American, British, German and other media. "It was incredible," Cook said, "We had no idea whether anybody really cared."