WASHINGTON — Late one Friday evening in 2014, Ohio’s environmental agency received word of a frightening test result from Toledo’s water supply: A toxic greenish substance had rendered the drinking water of half a million Toledo residents unsafe to drink.

“Immediately we reached out to the Environmental Protection Agency,” stated Craig Butler, the director of Ohio’s environmental agency. “Because of the scale of the difficulty, and the technical understanding essential, we necessary their knowledge.”

State officials flew water samples from Toledo to an E.P.A. laboratory in Cincinnati, where employees scientists identified the substance as microcystin, a uncommon but toxic substance that is made by algae blooms in water and causes liver damage in humans.

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The sources to respond to those emergencies, along with a lot of the other state-level perform performed by the agency, would be eliminated or sharply reduced by President Trump’s proposed budget for fiscal 2018, which cuts the E.P.A. by 31 percent, much more than any other agency.

Whilst the agency might be recognized for sweeping regulations to curb climate adjust, increase auto fuel efficiency or mandate smokestack controls, the agency’s bread and butter is much more prosaic. The employees and scientists at its regional offices and laboratories across the country often respond to emergency calls from city and state officials: a December 2016 chemical leak from an asphalt plant into the water supply of Corpus Christi, Tex. airborne drifts final summer in southern Missouri of dicamba, an herbicide that damages non-genetically modified crops a 2014 fire at a perfume factory in Bridgeport, Conn., that spewed hazardous chemical substances into the surrounding neighborhood.

Funds to respond to many of these calls would no longer be offered beneath Mr. Trump’s spending budget. He proposed lowering the agency’s $ eight.1 billion budget to $ five.7 billion, and cutting 3,200 jobs from the its employees of 15,000.

The proposal appears to be a realization of the federalist philosophy of the agency’s new administrator, Scott Pruitt, who has ardently championed states’ rights. He has stated repeatedly that he desires to pare down the agency’s overreaching federal authority and return the operate of environmental regulation to states.

But former E.P.A. officials say that in the case of responding to emergencies like the 1 that polluted Toledo’s water supply, states frequently lack the experience and resources of the federal government.

“What he fails to realize is that states do not have the technical capability to do some of this work,” said Gina McCarthy, who led the agency under the Obama administration.

Even in states like Ohio, which voted for Mr. Trump, officials like Mr. Davis say they are deeply concerned by the president’s proposed cuts to the agency.

Almost half of its present funding is passed directly to state environmental agencies. More than all, about a third of all state funding for environmental regulation is supplied by the E.P.A., according to an analysis by the Environmental Council of the States, a nonpartisan group that represents state environmental agencies.

That funding is utilized to enforce federal environmental laws at the state level. If that federal funding is reduce, “it is incredibly unlikely that states would be in a position to make up the funding,” mentioned Alexandra Dunn, the executive director of that group.

If federal funding for states to enact regulations and respond to emergencies is cut, authorities say, it could be hard for states to make up the distinction.

“I’m a huge fan of cooperative federalism,” Mr. Davis stated. “This procedure of reviewing the federal price range and removing programs that are duplicative is entirely appropriate.”

But he added, “Where that message conflicts with the president’s budget is where they say, ‘Hey, states, we want you to do this function, but we’re going to cut your price range to do it.’”