A group of major American engineering firms hoping to assist in the cleanup of the stricken Fukushima Daiichi nuclear power plant in Japan have hired a Washington lobbyist to help them get the ball rolling.

Omer F. Brown, a lawyer who specializes in nuclear energy and risk management, registered Monday to lobby on behalf of the seven companies, which have formed a coalition called the Fukushima Nuclear Assistance Group.

The companies want the International Atomic Energy Agency to invoke a treaty adopted more than two decades ago that would provide a framework for addressing liability claims that come up during their work on the dangerous site, which was devastated by an earthquake and tsunami in March.

Much as homeowner’s insurance doesn’t cover floods, the insurance that the operators of Fukushima purchased didn’t cover earthquakes, and American companies are reluctant to work there without some sense of who would cover the costs of a lawsuit.

“You can’t get insurance for this type of risk,” Brown said. “It’s a way that the companies can protect themselves if they get sued by employees or any other third party.”

The Japanese government has asked several American companies for technical assistance, said a spokesman for the Nuclear Energy Institute, which represents the nuclear industry in Washington.

Brown would not specify which companies are part of the coalition, but he currently represents major companies involved in the cleanup, including Westinghouse Electric Co., which is majority-owned by the Japanese company Toshiba, and Babcock & Wilcox Co. Engineers at both companies are already collaborating with Japanese engineers from afar to figure out how to dismantle the plant’s damaged reactors, according to news reports.

The United States, Japan and several other countries signed the IAEA treaty in 1986 after the Chernobyl nuclear accident in Ukraine, but it has never been used.

Brown will work with the Energy Department, where he used to work as a trial lawyer, and the State Department as the agencies decide whether to invoke the treaty and hammer out the details, including whether the Japanese government needs to write a formal request for assistance and who would pay for any claims that arise. Brown said that he will not lobby Congress on the issue.