By Taiga Uranaka and Yoko Nishikawa
TOKYO (Reuters) - Engineers enjoyed some success in their mission to stop disaster at Japan's tsunami-damaged power plant, though evidence of small radiation leaks highlighted perils from the world's worst nuclear crisis since Chernobyl 25 years ago.
Three hundred technicians have been battling inside a danger zone to salvage the six-reactor Fukushima plant since it was hit by an earthquake and tsunami that also killed 7,508 people and left 11,700 more missing in northeast Japan.
The unprecedented multiple crisis will cost the world's third largest economy nearly $200 billion in Japan's biggest reconstruction push since post-World War II.
It has also set back nuclear power plans the world over.
Encouragingly for Japanese transfixed on the work at Fukushima, the situation at the most critical reactor -- No. 3 which contains highly toxic plutonium -- appeared to come back from the brink after fire trucks doused it for hours.
Work also advanced on bringing power back to water pumps used to cool overheating nuclear fuel.
"We are making progress ... (but) we shouldn't be too optimistic," said Hidehiko Nishiyama, deputy-generalat Japan's Nuclear Safety Agency.
Engineers attached a power cable to the No.1 and No. 2 reactors, hoping to restore electricity later in the day. They also hope to reach No. 3 and 4 soon to test turning the pumps on.
If successful, that could be a turning point in a crisis already rated as bad as America's Three Mile Island accident in 1979. If not, drastic measures may be required such as burying the plant in sand and concrete as happened at Chernobyl after the world's worst nuclear reactor disaster in 1986.
Cooling systems have been restored at the least critical of the six reactors, No. 5 and 6, using diesel generators.
"It appears that the situation has somewhat stabilized but it is still very severe," said Bo Stromberg, an analyst at the Swedish Radiation Safety Authority.
On the negative side, evidence has begun emerging of radiation leaks from the plant, including into food and water.
Though public fear of radiation runs deep, and anxiety has spread as far as the Pacific-facing side of the United States, health officials say levels so far are not alarming.
Traces exceeding national safety standards were, though found in milk from a farm about 30 km (18 miles) from the plant and spinach grown in neighboring Ibaraki prefecture.
TAP WATER AFFECTED
Tiny levels of radioactive iodine have also been found in tap water in Tokyo, one of the world's largest cities about 240 km (150 miles) to south. Many tourists and expatriates have already left and residents are generally staying indoors.
The sample contained 1.5 becquerals per kg of iodine 131, well below the tolerable limit for food and drink of 300 becquerals per kg, the government said.
Japan said the traces so far found posed no risks.
Yet U.N. atomic watchdog the International Atomic Energy Agency said Japan was considering whether to halt all food product sales from Fukushima prefecture.
The first discovery of contaminated food since the March 11 disaster is likely to heighten scrutiny of Japanese food exports, especially in Asia, their biggest market.
Prime Minister Naoto Kan, who has kept a low profile during the crisis except for shouting at plant operator Tokyo Electric Power Co (TEPCO), sounded out the opposition about forming a government of national unity to deal with the crisis.
But the largest opposition party rejected that.
Showing the incredible power of the 9.0 magnitude earthquake, the largest in tremor-prone Japan's recorded history, Oshika peninsula in Miyagi prefecture shifted a whole 5.3 metres (17 ft) east and its land sank 1.2 metres (4 ft).
In contrast to the generally negative images so far, one video emerged showing the crew of a Japanese coastguard vessel successfully riding a massive wave by turning the bow directly at the wall of waters.
The quake and ensuing 10-meter high tsunami devastated Japan's north east coastal region, wiping towns off the map and making some 360,000 people homeless in a test for the Asian nation's reputation for resilience and social cohesion.
Food, water, medicine and fuel are in short supply in some parts, and near-freezing temperatures are not helping.
The grim search for bodies continues.
"This morning my next door neighbor came crying to me that she still can't find her husband. All I could tell her was, 'We'll do our best, so just hold on a little longer,'" said fire brigade officer Takao Sato in the disaster zone.
About 257,000 households in the north still have no electricity and at least one million lack running water.
In the face of mounting criticism, plant operator TEPCO's president issued a public apology for "causing such great concern and nuisance."
The crisis has been an unwelcome reminder for Japanese of their previous nuclear nightmare, the 1945 atomic bombs in Hiroshima and Nagasaki.
(Additional reporting by Nathan Layne, Kiyoshi Takenaka, Ealine Lies Mayumi Negishi, Tomasz Janowski in Tokyo, and Yoko Kubota and Chang-ran Kim in Rikuzentakata; Alister Doyle in Oslo; Writing by Andrew Cawthorne and Jason Szep. Editing by Jeremy Laurence.)