Massachusetts-based iRobot Inc. sent two Packbot and two Warrior robots to Japan to help measure radiation in contaminated areas. (Mike Fein/BLOOMBERG)

Inside a nondescript warehouse south of Mannheim, Germany, a dozen robots, ranging in size from a low-slung inspection bot no bigger than a toy wagon to a 22-ton Caterpillar excavator, stand ready to respond to a nuclear emergency. With their electronics hardened to withstand radiation, the versatile machines can handle fuel rods as well as monitor doses that would kill a human engineer.

A similar robotic quick-response squad is housed near the Chinon nuclear power plant in France.

But in Japan, where the Fu­kushima Daiichi nuclear crisis drags into its third week, the question is: Where are the robots?

The answer is disquieting, say Japan’s top roboticists. Instead of building robots that go where humans never could, this country renowned for its robotics expertise invested in machines that do things that humans can already do — like talk, dance, play the violin and preside over weddings.

“The government believed this accident wouldn’t happen,” said Hirose Shigeo, a robotics researcher at the Tokyo Institute of Technology. “Most of the robot experts are concentrating on humanoid [robots] and home use.”

“We should have focused on response and disaster-mitigation robots,” said Satoshi Tadokoro, who builds search-and-rescue robots at Tohoku University in Sendai. “The Ministry of Economy, Trade and Industry did not do that. The [power] companies did not do that. It is very strange and inappropriate.”

After a 1999 accident at a nuclear fuel processing facility in Tokai in which two workers died from radiation exposure, the Japanese government and the company operating the facility began developing radiation-resistant robots. But after a year, the trade ministry halted the project, said Shigeo and Tadokoro.

Another Japanese agency, the Nuclear Safety Technology Center, constructed two robots equipped with cameras and hazardous-materials monitors. One, called Monirobo, was dispatched to Fukushima last week, according to Japanese news reports. But representatives of Tokyo Electric Power Co., which operates the Daiichi facility, aren’t saying how, or even whether, the robot is being used on-site.

The need for robots that can withstand high radiation was made even more evident over the weekend after two workers at Daiichi were hospitalized after wading in radioactive water. Robots sent to the site early in the crisis could have guided key decisions by providing vital data on damage to the facility’s reactors and adjacent pools of used uranium fuel.

Instead, official statements from Tepco convey uncertainty about the extent of damage. And the International Atomic Energy Agency has repeatedly pushed for better information.

Shigeo said a robot developed in his lab, called Helios IX, could fill the reconnaissance niche. The machine can climb stairs, open doors, and monitor temperature and radiation. If its cameras aimed at the spent fuel pools, they could show whether water cannons operated by ground crews were refilling the pools or simply splashing streams onto the floor.

After the crisis began more than two weeks ago, Shigeo upgraded the radio communications on Helios IX so it can be guided from longer distances and through the heavy concrete of the Daiichi plant. So far, though, no one has requested his help — or that of his robot.

Another reconnaissance robot, built by Tadokoro and named Quince, may be called into action. The Tokyo Fire Department, which has sent vehicles and workers to Daiichi, is evaluating how the low-slung, tank-tracked machine could assist, Tadokoro said.

American robots are being enlisted as well. A Massachusetts company, iRobot, known for its Roomba vacuum cleaners, sent four of its heavier-duty robots to Fukushima, said Joseph W. Dyer, the company’s chief operating officer. Citing the sensitivity of the situation, Dyer declined to discuss which operations the robots might be involved in or whether the Japanese government had requested the shipment.

On Friday, a spokeswoman for the Department of Energy said the agency was evaluating its robotic inventory at the request of the Japanese government. The department has built several remotely operated robots to clean up radioactive waste from former nuclear-fuel processing facilities at its Hanford Site in Washington state and Savannah River Site in South Carolina.

Despite these investments, France (which derives about 80 percent of its electricity from nuclear power), and Germany (25 percent) are the only countries with at-the-ready robots designed for nuclear disasters. The nuclear power industry in each country has funded the operations for decades.

In the United States, the government and the nuclear industry have instead been reactive, building a handful of robots for specific nuclear tasks — but only after accidents.

Four years after the 1979 Three Mile Island crisis in Pennsylvania, the team tasked with cleaning up the mess tapped a robotics pioneer at Carnegie Mellon University, William L. “Red” Whittaker. Whittaker’s lab quickly built two robots that provided the first views of the damaged reactor. One of the machines ultimately spent four years chewing on the building’s irradiated concrete walls, sucking up radioactive water and scooping up partially melted uranium fuel.

After that success, Whittaker co-founded a company called RedZone Robotics, which in 1998 built a robot for the Chernobyl disaster in the Ukraine. But a few years later the company abandoned the market, said chief executive Eric C. Close. “It’s very hard to have a business model that waits for nuclear disaster,” he said. RedZone instead builds snake-like robots that navigate and maintain sewage pipes.

Tadokoro said that after Japan’s 1999 nuclear accident, regulatory officials and the country’s power companies discussed developing a robot response squad like those in Europe. It never happened.

“A decision was made not to invest,” Tadokoro said. “It’s very frustrating.”