(New throughout, adds comment from FirstEnergy, background on Exelon settlement and on nuclear subsidies)

July 21 (Reuters) - Ohio House Speaker Larry Householder, a Republican, and four other men tied to state politics were arrested on Tuesday in a $60 million federal bribery case stemming from a bill passed last year to bail out the state's nuclear power plants, a U.S. prosecutor said.

Shares of FirstEnergy Corp fell 17% after U.S. Attorney for the Southern District of Ohio David DeVillers revealed what he called the largest bribery and money-laundering scheme in state history. He said the five men were charged with conspiracy to commit racketeering.

While DeVillers did not identify the company involved, Akron-based FirstEnergy operates the state's two nuclear plants. The company, he said, gave $60 million to Generation Now, a political nonprofit operated by the five men, funds used for lobbying that secured passage of a controversial $1.5 billion bill that bailed out the plants, he said. "These allegations were bribery pure and simple," DeVillers said. FirstEnergy said in a release it had received subpoenas in connection with the investigation, was reviewing details and intends to fully cooperate with the probe.

Republican Ohio Governor Mike DeWine called for Householder to resign immediately.

In recent years, FirstEnergy was among several companies that have lobbied state and federal officials to get subsidies to keep reactors in service. Aging nuclear plants have suffered from higher security costs and competition from power plants that burn cheaper natural gas.

FirstEnergy in early 2018 asked the U.S. Department of Energy to intervene in markets by using emergency powers to direct grid operators to buy electricity from coal and nuclear plants. U.S. President Donald Trump directed then-Energy Secretary Rick Perry to use an independent office of the department's authority in a way that would help plants like those operated by FirstEnergy.

Federal energy regulators rejected those overtures, instead taking up a study of how to make the electrical grid more resilient.

The companies claimed the plants were needed to support state clean energy programs and without those reactors several states would have had a hard time meeting their clean energy goals.

This month, Exelon Corp's unit ComEd agreed to pay $200 million to resolve a U.S. Department of Justice probe over lobbying practices in Illinois.

Former Ohio Republican Party Chairman Matt Borges and longtime Householder adviser Jeff Longstreth along with lobbyists Juan Cespedes and Neil Clark were also charged on Tuesday. Householder's office was not available for comment. (Reporting by Brendan O'Brien in Chicago, Timothy Gardner in Washington and Scott DiSavino in New York; editing by Bill Tarrant, Tom Brown and David Gregorio)