This new alignment of power is causing alarm among not only environmental groups but also other — mostly liberal — advocates who have spent much of the past eight years pushing for new rules to cover Wall Street banks, broadband providers, teacher preparation requirements, prepaid credit cards and even companies that sell high-calorie foods in vending machines.

All of these measures, and many others, now stand a chance of being reversed, watered down or blocked.

“For the last several years, whenever Congress would concoct some way to roll back a rule protecting clean air or clean water or undermine the fight against climate change, we always felt confident as we had an adult in charge at the White House,” said Michael Brune, executive director of the Sierra Club, an environmental group. “Now, what used to be a wish list of the oil and coal and gas industry has become the to-do list for Congress and the White House.”

For Republicans, these first moves are the easy part, made possible by a law that gives Congress the power to reverse regulations within 60 legislative days with a simple majority vote in the House and Senate. Other Republican efforts to exploit this 20-year-old law — which until this week had been used only once to nullify a new rule — were thwarted five times with vetoes by President Obama since 2015.

Once the 60-day window expires, Republicans will have a harder time reversing Mr. Obama’s regulations, but will still have tools at their disposal, including cutting financing for the enforcement of rules, issuing new rules that are weaker, or negotiating with Democrats to pass new legislation.

They have bold ambitions, including rescinding a rule enacted by the Obama administration that could close dozens of coal burning power plants, and another that would extend overtime pay eligibility to an estimated four million Americans.

At a private meeting on Thursday hosted by the National Association of Manufacturers, a trade group, a senior White House adviser provided a plan on how the administration would handle efforts to curtail environmental regulations beyond the initial rush now underway to nullify recently adopted rules, said an energy industry executive who participated in the meeting and spoke on the condition of anonymity because details were confidential.