TOKYO (AP) _ Three officials were relieved of their posts today because of attempts to cover up the seriousness of a recent accident at an experimental breeder nuclear reactor.

No one was reported injured in the accident, which has triggered renewed opposition to Japan's ambitious plans to depend on breeder reactors for its electric power needs. Breeder reactors are capable of producing more plutonium than they use.

The government agency that runs the $5.6 billion Monju reactor in western Japan said the men were being disciplined for their handling of the Dec. 8 accident, when tons of caustic liquid sodium coolant leaked.

Officials at the plant heavily edited a videotape taken after the accident to conceal the most serious damage, and hid a second videotape.

The cover-up angered Japan's government as well as local residents, and the Science and Technology Agency took over the inquiry into the accident from the governmental Power Reactor and Nuclear Fuel Development Corp., which runs the reactor.

Officials of the corporation, called Donen in Japanese, said the three executives will be reassigned to other Donen ventures after the government inquiry into the accident is completed.

They said the Donen director in charge of Monju's operations will also be replaced pending approval by Prime Minister Tomiichi Murayama.

The reshuffle is intended to ``radically revise the system and structure of responsibility at the Monju plant,'' Donen said.

The plant is located in Tsuruga in Fukui Prefecture on the Sea of Japan, about 220 miles west of Tokyo.

Fukui Governor Yukio Kurita told Yasuoki Urano, the Science and Technology Agency minister, that Fukui citizens ``feel betrayed'' because of the plant's handling of the accident.

``I urged the minister to deal with the matter strictly to ensure the plant's safety and reliability,'' Kurita told reporters in Tokyo. ``The operation of Monju should not be resumed until we are satisfied with measures to ensure its safety.''

The plant began generating electricity in August and had been running at 40 percent of its full capacity of 280,000 kilowatts. It was scheduled to go into full production next June.

Japan was among several nations looking into plutonium breeder reactors in the 1970s, when uranium was more expensive.

But the danger of working with plutonium, the difficulty of cooling the reactor, and higher construction costs have convinced most countries to scrap their breeder reactor plans.

Resource-poor Japan is now the only major industrialized nation pursuing the technology for commercial use.

Monju is named after the Buddhist deity of wisdom.