Japan will power down its last operating nuclear reactor this weekend, finalizing the country’s sudden turn away from a once-preferred energy source and leaving it nuclear-free for the first time since 1966.

On Saturday, at the Tomari atomic power plant in Hokkaido, engineers will begin work to shut down the No. 3 reactor, which is due for its regular maintenance checkup. By Sunday, the unit will officially come offline, the plant operator said.

The break from nuclear power is less a matter of policy than political paralysis. Japan’s central government has recommitted to nuclear power in the wake of last year’s triple meltdown at Fukushima Daiichi, but those authorities have not convinced host communities and provincial governors that nuclear power is necessary — or that a tarnished and as-yet-unreformed regulatory agency is up to the job of ensuring safety.

Because Japan depends on local consensus for its nuclear decisions, those maintenance checkups — mandated every 13 months — have turned into indefinite shutdowns, and resource-poor Japan has scrambled to import costlier fossil fuels to fill the energy void.

Before the Fukushima accident, Japan operated 54 commercial reactors, which accounted for about one-third of the country’s energy supply. Seventeen of those reactors were damaged by the March 11 earthquake and tsunami or shut down over the past year because of government request. Thirty-six others were shuttered after inspections and have not been restarted.

Political and business leaders fear the economic toll of summer energy shortages, but critics of Japan’s nuclear policy say authorities in Tokyo have not done enough to improve nuclear safety standards and break up the traditionally cozy ties between government and industry.

Japan’s cabinet said last year that the country needed a new nuclear safety agency that is “trusted domestically and internationally,” and Prime Minister Yoshihiko Noda had hoped to have the new agency in place by April 1. But politicians are still squabbling about how the new agency will operate and the extent to which it will coordinate with the cabinet. Experts say it could be months before Japan creates the new watchdog.

Meanwhile, Noda and industry minister Yukio Edano have been pushing to restart two reactors in sparsely populated Fukui prefecture, north of Osaka. The Nos. 3 and 4 units at the Ohi nuclear plant have already passed stress tests — computer simulations designed to test defenses against emergency scenarios. And government officials made several trips from Tokyo last month to meet with local governors and townspeople, arguing for a restart.

The Ohi reactors are operated by the Kansai Electric Power Co., the Japanese utility most dependent on nuclear power. Without restarts, the utility company — providing power to Japan’s industrial heart — will be 16.3 percent short of peak demand this summer, according to government-released data.

“If a reliable, stable supply of electricity is not certain, domestic manufacturers have to think about moving to other countries, which in turn would lead to a hollowing out of industry and a loss of domestic employment,” Takashi Imai, chairman of the Japan Atomic Industrial Forum, said at a conference last month. “The national economy would clearly suffer.”

But a deep resistance toward nuclear power carries on in the wake of last year’s Fukushima crisis, which displaced roughly 100,000 people. Some 67 percent in Fukui prefecture, according to a recent Asahi newspaper poll, oppose the restart of nuclear reactors. Sixty-three percent say they do not trust the government’s safety standards.

The mayor of Osaka, Toru Hashimoto, one of Japan’s highest-profile politicians, has also become a torchbearer for the anti-nuclear group. He recently knocked the central government, saying it was “absolutely unreasonable” that authorities have deemed it safe to reactivate the Ohi reactors.

Hashimoto said Japan must create a new nuclear watchdog and improve safety standards before reconsidering atomic power.