BERLIN (Reuters) - Half a life-time ago, artist Yoko Ono lay in an Amsterdam hotel bed with husband John Lennon, staging a week-long "bed-in" for peace and feeling they were very alone in their activism.

Today, Ono, whose own energy for campaigning has never tired, sees a world full of activists, maintaining her energy and faith in humanity.

"When John and I did the bed-in, not many people were with us. But now there are so many activists, I don't know anyone who is not an activist," she told Reuters in an interview in Berlin on Monday, her 80th birthday.

"Even the corporations - John always used to say the corporations need to be with us... Corporations now say 10-20 percent of their profits will go to such and such charity. They have to do that almost for people to feel good about it."

The late Beatle and Ono's 1969 bed-in to protest against the Vietnam war was repeated in Montreal, Canada. Press attention was huge, but much of it was mocking.

Ono, who gave a sell-out concert in Berlin on Sunday alongside their son Sean Lennon which closed with the anthem "Give peace a chance", said it was still critical to stand up for peace despite new conflicts in the intervening decades.

"I don't want to be drowning in sadness. I think we have to stand and up and change the world," she said.

The artist, born to a wealthy Japanese family in Tokyo in 1933, has recently become a passionate opponent of fracking, a controversial procedure which has sharply lifted energy output in the United States but which critics fear pollutes drinking water deep underground and could increase earthquake risks.

"Fracking is an incredible risk to the human race, I don't know why they even thought of doing it," she said.

Ono, whose birthday is being marked by a major retrospective of her work in Frankfurt, said she feels she is becoming freer in her art.

"My attitude has changed... I'm allowing things to happen in a way I hadn't planned before," she said.

Asked about her feelings on becoming an octogenarian, she said: "I'm surprised. It is a miracle in a sense that I am 80, I am proud about it. Not everybody gets there."

(Reporting by Alexandra Hudson, editing by Gareth Jones and Paul Casciato)