Protesters take part in an anti-nuclear demonstration demanding a stop to the resumption of nuclear power operations in Tokyo July 1, 2012. (Yuriko Nakao/Reuters)

Protesters thronged the wide streets in front of the prime minister’s office in Tokyo over the weekend, and across the country they gathered about a quarter-mile from the entrance of a nuclear plant. They shouted “No to the restart” and parked cars in front of the plant’s access road to block workers from coming or going, according to Japanese media.

But the workers were already inside.

At the Ohi nuclear facility on Japan’s western shoreline Sunday, those workers went through the technical steps to reboot a reactor, the first to come back online since last year’s massive nuclear accident at Fukushima Daiichi.

The restart at Ohi — with potentially more to follow — will avert dire power shortages and sustain the economy, Prime Minister Yoshihiko Noda has told the nation. But the restart also has divided the country, staging an increasingly hostile showdown between the government and those doubtful about its atomic safety claims.

Some political experts thought that Noda’s announcement two weeks ago about the restart of two reactors at Ohi — the No. 4 unit is scheduled to restart later this month — would quiet public opposition. Instead, Noda’s announcement fomented it, and social-media-organized protests that once drew hundreds now draw thousands. A rally Friday in front of Noda’s office drew 17,000, according to police; organizers put the number around 200,000.

The central government has so far given no indication that the public display will cause a rethinking of its nuclear restart efforts. Wide-scale protests are rare in this country, where people traditionally comply with authority figures, and Noda, who is also pushing for a consumption tax increase, faces a backlash for his pro-nuclear stance.

In a June 5 Pew Research Center poll, 70 percent of Japanese respondents said they favor a reduction in the country’s reliance on nuclear power. The government, before calling for the restart, received approvals from local and regional officials near Ohi, a process that required months of persuasion.

Engineers at Ohi on Sunday night pulled out the control rods that prevent nuclear fission. By Wednesday, according to Japan’s Kyodo news agency, the 1,180-megawatt reactor will begin transmitting power.

Before the series of meltdowns at the Fukushima plant, which forced the evacuation of more than 100,000 people, Japan depended on its 54 reactors for about one-third of its energy. But in the wake of the accident, those reactors steadily went offline, either because of safety concerns or for routine maintenance checks. In early May, the final reactor in Hokkaido went offline and the country briefly became nuclear free.

Noda became a voice for the restart, saying that a failure to restart the reactors would jeopardize life as Japanese knew it. The government predicted energy shortages during the sweltering summer — nearly 15 percent in one region, Kansai, which had been particularly atomic-dependent. The government picked reactors No. 3 and No. 4 at Ohi for the first to restart because they supplied the Kansai region and because they had already passed stress tests to gauge their response to disasters.

The restart comes at a time when policymakers here are planning the country’s energy future. The Energy and Environment Council is debating three options: By 2030, nuclear power will account either for 20 to 25 percent of Japan’s total electricity output, 15 percent, or zero percent. The council is supposed to reach a decision in August, Japanese media have said.