Toyota Motor Corp. and Nissan Motor Co. may forecast first-half losses and continuing sales declines as the two biggest Japanese automakers struggle to restore full production disrupted by a record earthquake.

Toyota, the automaker most affected by the earthquake in March, may post net losses of 155 billion yen ($1.9 billion) in the three months ending June 30 and 241 billion yen for the six months ending Sept. 30, according to the average of analysts’ estimates compiled by Bloomberg in the past four weeks. Nissan’s six-month net loss may be 48 billion yen, based on the estimates.

In the worst case, combined losses for the nation’s carmakers and suppliers may be “the biggest ever,” surpassing those at the time of the 2008 to 2009 financial crisis, Noriyuki Matsushima, an analyst in Tokyo at Citigroup Inc., said last week. Citigroup also downgraded Japan’s auto industry to “sell” from “buy” on April 8.

“Even if production comes back, demand for cars may not come back as people are still fearing radiation contamination and earthquake aftershocks are still going on,” said Yuuki Sakurai, president at Fukoku Capital Management Inc. in Tokyo.

Toyota, Nissan and Honda Motor Co. are working to restore full operations after the magnitude-9 temblor and tsunami damaged factories and caused parts and power shortages. The Toyota City, Japan-based company expects production may not return to normal until November or December.

Toyota’s American depositary receipts, each representing two ordinary shares, rose 48 cents to $80.16 at 4:15 p.m. in New York Stock Exchange composite trading. They’ve fallen 8.4 percent since March 10, the day before the earthquake.

Toyota’s vehicle sales in Japan plunged 69 percent last month, leading the eighth straight drop in the nation’s monthly auto deliveries after the earthquake shut down production and a government subsidy program ended.

Industrywide sales of cars, trucks and buses, excluding minicars, fell 51 percent from a year earlier to a record-low 108,824 vehicles in April, the Japan Automobile Dealers Association said in a statement today. Toyota’s deliveries fell to 35,557 vehicles, excluding Lexus-brand cars.

The industrywide total was the lowest for any month since 1968, when the association started tracking sales, while the 51 percent decline was the biggest for any month since May 1974.

Toyota is scheduled to report fourth-quarter and full-year earnings on May 11, followed by Nissan on May 12.

Keisuke Kirimoto, a spokesman for Toyota, said he couldn’t comment on earnings projections or on the scale of the impact from the March 11 earthquake relative to the financial crisis or last year’s record vehicle recalls by the company. He also declined to say whether Toyota will provide a half-year or full- year forecast next week. Toyota President Akio Toyoda on April 22 also declined to comment on the quake’s impact on earnings.

Mitsuru Yonekawa, a spokesman for Nissan, didn’t return calls made to his cellular phone.

All of Japan’s automakers halted production after the earthquake and tsunami damaged parts factories and power plants, causing shortages of components and electricity. Output disruptions are continuing at car factories in Japan and overseas.

Renesas Electronics Corp., a chipmaker that has 30 percent of the world market for microcontrollers used in cars, said April 22 it will restart production at a damaged factory on June 15, prompting Toyota to say car production will return to normal levels by the end of this year.

Citigroup’s Matsushima said output reductions by Japanese carmakers may continue until April 2012.

“Japan’s automakers will run out of inventory at overseas plants in the second quarter, so figures for that quarter may be lower than those in the first quarter, even as they begin to raise production levels,” he said.

During the financial crisis, Toyota’s net loss for the year ended March 2009 was 436.9 billion yen, while Nissan’s was 233.7 billion yen. Honda, Japan’s third-largest carmaker, reported a profit of 137 billion yen.

Even before the earthquake, the dealers association had forecast a 13 percent drop in vehicle sales in Japan to 2.8 million this year, after the government phased out subsidies for fuel-efficient models in September.

Toyota resumed output at all Japan plants on April 18 at half capacity. The company may lose production of 300,000 vehicles in Japan and 100,000 overseas through the end of April due to quake-related shutdowns, Executive Vice President Atsushi Niimi said April 22. He said the company may miss its global production target of 7.7 million vehicles for the 2011 calendar year.

Last month in Shanghai, Toyota said it may not be able to meet its China sales target of more than 900,000 vehicles this year due to the impact of the natural disaster.

The earthquake and tsunami were another blow to the company after Toyoda’s first full year on the job was consumed by recalls that totaled more than 10 million vehicles, ranging from luxury Lexus sport-utility vehicles to Prius hybrids. Toyoda, 54, was called to testify before the U.S. Congress on the automaker’s safety record, and the company’s sales slumped.

Toyota called back millions of U.S. vehicles in 2009 and 2010, mostly for defects related to unintended acceleration. The carmaker also paid a record $48.8 million in fines for how some of the recalls were conducted. The recalls caused the company to briefly halt sales of some models in 2010 and contributed to its 0.4 percent U.S. sales decrease last year, the only decline among large automakers.

Even as parts suppliers recover, carmakers in Japan will suffer from power shortages after the March 11 disaster reduced the nation’s electricity-generating capacity, said Koji Endo, an analyst at Advanced Research Japan in Tokyo.

The impact from the earthquake is still less severe than that of the financial crisis, Endo said.

“The situation now is different because demand isn’t hurt at all,” he said. “Full-year earnings may not be that bad.”

For the fiscal year that ended March 31, Toyota earnings may more than double to 471 billion yen, according to the average of analysts’ estimates compiled by Bloomberg in the past four weeks. Nissan’s profit may rise sevenfold to 303 billion yen.