Gov. Andrew M. Cuomo signed a new state law Thursday directing Long Island’s 400 local governments and others across the state to develop savings plans to share services to ease the property tax burden on homeowners.

The law covers counties, towns, cities and villages, will create panels which locally will be led by the Nassau and Suffolk county executives, to develop joint savings plans, hold public hearings and require local officials to justify their decisions to reject parts of the plans.

“I don’t accept the premise you are running a perfect organization,” Cuomo told a crowd of more than 120 officials and other guests at Laborers Local 66 in Melville. “I don’t believe there aren’t more efficiencies one can find from government ... There’s always more.”

Cuomo said the law will force local officials to “have a conversation that has never happened” about how to share equipment such as heavy trucks, pool purchases and purchase insurance jointly.

Instead of “400 individual fiefdoms,” Cuomo said governments have to work together. “Not everyone has to do everything,” he said. “Not every government is a country unto itself.”

State officials say the law gives the executives the option of inviting representatives of school districts, which account for nearly 70 percent of the property tax levy, and other taxing jurisdictions to take part in the process.

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Suffolk County Executive Steve Bellone said he will invite school officials to participate; Nassau County Executive Edward Mangano, who backs the law, did not return calls for comment.

Cuomo said if local governments statewide can cut spending by even three percent, taxpayers could save $384 million. He said the state will match savings achieved by local governments after the savings plans go into effect for 2018.

Cuomo said the new law is “even more critical” given a proposal by President Donald Trump to end deductions for state and local taxes, which Cuomo said could cost 950,000 local taxpayers a total of $4.3 billion, or $4,600 per taxpayer.

Suffolk Legis. Kevin McCaffrey (R-Lindenhurst), GOP caucus leader, said the new law is “worth a try.” However, “the county needs to first show that it can handle its own finances before it tries cost saving in other levels of government,” McCaffrey said.

The Suffolk Village Officials Association criticized the law, saying the biggest fiscal problem is the “myriad of costly unfunded state mandates.”

Charles Russo, president of the Suffolk School Superintendents Association, said he was unaware local districts could be included in the process. But he said schools are “always looking for cost savings methods” and most already share services.

Under the legislation, county executives must form panels made up of town supervisors and city and village mayors to submit preliminary savings plans by Aug. 1. The panels then would hold at least three public hearings, and would vote on their final plans by Sept. 15.

Elected officials and others who volunteer to become involved in the process can reject portions of the plans, but will have to provide written explanations for their reasons. By Oct. 15, the county must file the final plan with the state and spell out specific saving to taxpayers.

“It’s a good concept, but it’s going to be challenging,” said Presiding Officer DuWayne Gregory (D-Copiague). “The challenge is turf wars. But if people can look to the greater good we can accomplish something for taxpayers.”