Gov. Jerry Brown, a Democrat, said in an interview that the rush by Republicans to pass a bill made it impossible to judge how much the legislation could hurt the state.

“I can’t penetrate the inner motivations of the Republican leadership,” Mr. Brown said. “But I will say there is something very odd about their rushing this very gigantic tax proposal through Congress without serious transparency or debate. They are doing so primarily, it seems, to reward their corporate donors.”

“I don’t like this way to govern in a democracy,” he said.

Representative Darrell Issa, whose San Diego County district is among the most vulnerable Republican seats in the state, said he would oppose the bill.

“I cannot endorse changes that may make the tremendous burden felt by California taxpayers even worse,” he said. “Tax reform should lower taxes for all taxpayers — regardless of where they live.”

But so far, Mr. Issa’s opposition appears singular within the state’s Republican delegation, at least among those who will offer comment. Representative Kevin McCarthy, the majority leader, who represents a Central Valley district, strongly backed the effort. He said other parts of the bill — such as increasing the standard deduction and eliminating the alternative minimum tax — would help California taxpayers who were, he said, saddled with high state taxes.

State Senator Jeff Stone, a Republican, also endorsed the effort, saying it would bring welcome relief to California taxpayers.

“The Democrats keep raising taxes in California,” he said. “It’s about time the federal government stops letting them off the hook by giving them cover with an overly complicated federal tax system.”