LOS ANGELES — In a major setback for environmental advocates in California, Gov. Jerry Brown and Senate Democrats abandoned a 50 percent cut in petroleum use by 2030 that was a centerpiece of emissions legislation, blaming an intense campaign against the mandate by the oil industry.

The measure, the latest and most ambitious part of a series of legislation and regulations by the state to significantly curb greenhouse gas emissions over the next 35 years, passed the Democratic-controlled Senate but faced almost certain defeat in the Assembly, where Democrats are also in control but tend to be more moderate and represent economically struggling parts of the state. Opponents had warned that the 50 percent mandate would result in higher fuel and electricity costs; the oil industry, in its advertisements, asserted that it could lead to fuel rationing and bans on sport utility vehicles.

Backers described those allegations as false — the bill does not mention rationing or any other specific measures — but those arguments seemed to go far in coalescing opposition to the bill. The decision on how to carry out the proposed cuts would have been left to the state’s Air Resources Board, a matter of strong concern to many lawmakers.

“Big Oil might be on the right side of their shareholder reports, but we’re on the right side of history,” Kevin de Leon, the Senate Democratic leader and main champion of the bill, said in announcing the decision. “And ultimately, California is going to demand that an industry which represents most of the problem has an economic and moral duty to be part of the solution.”