TOKYO (AP) _ Thousands of Japanese demonstrated against nuclear power on Sunday, the third anniversary of the Soviet Union's disastrous accident at Chernobyl.

Organizers said about 3,000 people, some chanting ''Protect our children'' and ''Remove nuclear plants,'' marched in the rain in Kawasaki, just south of Tokyo, and gathered along the Tama River.

''We must be more sensitive against contamination and pollution, even if such struggles are held far away from metropolitan districts,'' Kohtaro Yamamoto said as he watched a concert that was part of the rally.

''Various signs indicate that a turning point in the anti-nuclear movement has been reached after the Chernobyl disaster,'' said Eriko Hirai, 32, a homemaker who joined in the protest.

The April 26, 1986, accident at the Chernobyl nuclear power plant sent a cloud of radiation over large parts of northern and central Europe, leading to bans on foodstuffs from several countries. Hundreds were hospitalized, including at least 31 who died from radiation-related injuries.

Elsewhere in Japan on Sunday, organizers said more than 1,000 people rallied in Osaka, Japan's second-largest city; 600 turned out in the central city of Nagoya; and 300 demonstrated in Kyoto in western Japan.

In the western port of Kobe, about 1,500 people demonstrated Saturday at the Kansai Electric Power Co.

Despite recent reductions in nuclear power development in some countries, Japan plans to produce more electricity with nuclear power to reduce reliance on oil imports. Nuclear plants now meet 28 percent of Japan's power needs, the government says. Utilities predict that share will rise to 36 percent by 1995.