The surprise closure of another Japanese nuclear plant, this time at the power supplier to the heart of the auto industry, threatens to dampen consumer sentiment and will provide car makers with yet another reason to produce fewer cars in Japan.

Chubu Electric Power <9502.T> agreed on Monday to close its Hamaoka plant in central Japan, raising concerns over the steady supply of power to its region, which is home to Toyota Motor Corp <7203.T> and other major manufacturers.

The shutdown was requested by the government, which singled out Hamaoka as particularly vulnerable to a major earthquake and tsunami, after the 9.0-magnitude quake on March 11 triggered a nuclear crisis in the northeast.

Output disruptions may not be large enough to delay the economic recovery nationwide because Chubu is taking steps to meet peak summer demand by boosting thermal energy and securing electricity from another utility in western Japan.

But in the longer run the lack of clarity about how the government's energy policy might change following the March 11 disaster could tempt Japanese manufacturers to move more production overseas and discourage private consumption.

We can rely on thermal power in the short term, but this raises costs and emissions, said Yasuo Yamamoto, senior economist at Mizuho Research Institute.

In the future, we're not sure what the government wants to do. The longer that uncertainty about the power supply continues, the more companies will start thinking about manufacturing overseas.

The Hamaoka plant, located about 200 km (120 miles) southwest of Tokyo, accounts for about 15 percent of its electricity output. Chubu in turn provides power to half of the 18 plants that make Toyota's vehicles in Japan, and all four of Suzuki Motor Corp's <7269.T> domestic car and motorcycle factories.

The coverage area also includes other auto plants including those of Honda Motor Co <7267.T> and Mitsubishi Motors Corp <7211.T>, but Toyota is most vulnerable given its heavy ratio of cars made domestically.

Toyota and Honda have been forced to operate at about half the levels planned before March 11 due to the shortage of components. They have forecast a return to normal production levels by the end of this year.

The Chubu region also includes a concentration of manufacturers in the flat panel display and semiconductor industries, such as Sharp Corp's <6753.T> Kameyama LCD factory and Toshiba Corp's <6502.T> Yokkaichi semiconductor plant.

Toyota, Suzuki and other car makers said they had no comment on how they would cope before Chubu Electric explains how it plans to make up for the power shortfall.

Replacing nuclear power with that produced by conventional thermal plants could increase electricity costs, but those make up only a small portion of automakers' costs, argues Nomura Securities auto analyst Masataka Kunugimoto.

What matters more, analysts say, is doubts about reliability of power supplies that could give automakers another reason -- in addition to a strong yen and cheaper labor abroad-- to shrink production volumes in Japan.

This raises a question of how you're going to split your domestic and overseas production, said Koji Endo, senior analyst at Advanced Research Japan.

Toyota and Nissan have publicly committed to a minimum level of domestic production to keep Japan's tradition of manufacturing alive, but questions surrounding energy policy could force a rethink, Endo said.

The shutdown's impact on households could be more direct and immediate. Power cuts or a rise in electricity bills could force households served by Chubu Electric to save more energy or spend less on everything else, damaging sentiment already depressed by radiation leaks from the Fukushima plant in the tsunami-ravaged northeast.

Private consumption accounts for more than 50 percent of gross domestic product and Japan's limping economy badly needs consumer spending to hold up.

Chubu Electric is likely to come up with a campaign to save power, which could depress private consumption, said Takuji Okubo, chief economist at Societe Generale Securities.

Companies should be able to cope, but weak consumer sentiment could become a national phenomenon.

(Editing by Nathan Layne and Tomasz Janowski)