Fifty years ago this month, President Richard Nixon signed one of the most effective laws ever written to protect the environment and strengthen democracy by ensuring that citizens would have a say over projects like highways and pipelines that directly affect their well-being.

Now President Trump is trying to cripple it.

New rules that he proposed on Thursday for carrying out the law would strike at the heart of the public’s right to know what our government is doing or failing to do on our behalf and to speak to the lasting impact those actions might have.

Often called the Magna Carta of environmental law, the 1970 National Environmental Policy Act requires that major energy and infrastructure projects receiving federal funding or requiring federal approval must undergo environmental reviews. Citizens have a right to weigh in on these proposals in hearings and through a public comment process.

Mr. Trump’s proposed changes would reduce the number of projects subject to such reviews, by setting new criteria for what qualifies as a major federal action requiring review by excluding projects deemed to be “minimal.” It’s not possible, from the vague language in the proposed rules, to predict which kinds of projects might escape reasonable review, but the enthusiastic response to the proposed changes from the oil, gas and construction industries offers a clue. As more projects are exempted, less information will be available about their potential impacts on communities and the environment.

And by relaxing language meant to prevent conflicts of interest, Mr. Trump’s rules would allow environmental reviews to be conducted by contractors with a financial interest in the project. That could give corporations more influence over how those reviews are written, increasing the chances of rosy reports that favor corporate interests.

The rules would enable fossil fuel companies and others to put their profits ahead of the public interest. Mr. Trump’s plan would also restrain the fight against climate change by removing a requirement to assess a project’s cumulative impacts, like the emission of greenhouse gases.

That’s a handout to the fossil fuel industry, which doesn’t want long-term climate impacts to be considered in decisions over whether to allow more coal to be mined from public lands, for example, or more oil drilled offshore.

Everyone who cares about public integrity and good governance, from any political party, should oppose this effort to surrender responsible public oversight to the ends of big polluters.

For half a century, the National Environmental Policy Act has guaranteed everyone affected by one of these projects — individuals, small-business owners, community activists, faith-based organizations, tourism groups, conservationists and others — a seat at the table.

The law lays out a process designed to expose a project’s potential pitfalls in advance, identify common ground and open the door to innovative solutions that can benefit all parties. It also requires the federal government to consider alternatives and mitigation for projects that threaten communities with lasting harm.

This is how a modern nation working to build a more just and equitable society blends public input with good governance to reach decisions that balance corporate interests with the broader good. Small wonder that some 160 other countries have emulated this model with laws of their own, seeking to replicate a process that has proved its worth time and again.

It resulted, for instance, in improved efficiency, navigational safety and wetlands protection at a major container terminal at the Port of Mobile, Ala.; important provisions for controlling erosion, protecting wildlife and restoring native trees and grass along a new highway through a national forest in Ohio; and the planting of vegetation to naturally filter runoff from a new medical facility in rural Virginia, reducing the risk of contamination to area groundwater sources.

That approach has been especially vital in the effort to confront environmental injustice. There’s a long and shameful practice in this country of steering big projects in or near low-income communities. The provisions of the National Environmental Policy Act help to level the playing field, ensuring that all citizens have the opportunity to address federal officials, through public hearings or written comments, to which federal agencies must respond.

In proposing to weaken the law, Mr. Trump argues that the new rules would speed the costly process of environmental review. “It takes 20 years,” he said Thursday in rolling out the proposed changes. “It takes 30 years. It takes numbers that nobody would even believe.”

Actually, the most common reason, by far, that major federal projects are delayed is a lack of funding, not regulatory review, a 2016 study for the Treasury Department of 40 major water and transportation projects found.

Not all federally approved or funded projects even end up receiving extensive environmental review. A new highway or power plant gets one, but resurfacing a road or putting up a fence to protect cultural resources does not. Of the thousands of projects that are funded or permitted by federal agencies each year, in fact, 95 percent are excluded from any detailed environmental assessment at all, according to a 2014 report by the Government Accountability Office. Less than 1 percent require full environmental impact statements, which take, on average, four and a half years to complete.

Nobody wants overregulation. But it can take time to gather critical information required to make informed decisions on projects that change entire landscapes. Better to get it right than to cut corners in ways that end up imposing even higher costs on everyone down the road.

We need to tell our representatives in Congress that we care about our right to know about what happens in our communities and our ability to speak out in ways that matter to protect the environment and public health. Don’t let the president turn back the clock five decades to a time when the government was inclined to give big industry a pass and let the people pay the price.

Sharon Buccino is the senior director of the lands division of the Natural Resources Defense Council, an environmental advocacy group.