The Supreme Court’s decision on Monday to allow the Trump administration to move ahead with its plans to restrict mail-in voting threatened to introduce confusion to the midterm elections as states grapple with how to respond.

The executive order at the center of the ruling directs federal agencies to create “state citizenship lists” of eligible voters. Those would be sent to state elections officials and to the Postal Service, which could refuse to mail ballots for anyone whose name was not listed.

But some state elections officials and experts said on Tuesday that it was unclear whether the new rules could be put in place by the November elections. Even the Postal Service, in a final rule published on Friday, noted that “delaying the effective date would jeopardize implementation of this rule in time for the 2026 general election” on Nov. 3.

California and several other states are expected to file a lawsuit this week challenging the Postal Service’s final rule. Other states, including Oregon and Colorado, signaled they expect voting for November to proceed as expected. Some, like North Carolina, said they were monitoring the tangle of litigation.

“I have no doubt that our election is going to go on as normal: Safe, secure and transparent as always,” said Dag Robinson, who is the county clerk in rural Harney County, Ore., and the president of the Oregon Association of County Clerks.

The Supreme Court’s decision adds to a chaotic pileup of legal rulings and challenges surrounding the nation’s electoral system as control of Congress hinges on just a few seats.

Every state has some form of mail-in or absentee voting. Many of the states with the highest rates of mail voting oppose the executive order.

Some states have already designed and printed ballots, a costly endeavor, and the first absentee ballots will be sent starting Sept. 4.

Stuart Holmes, Washington State’s elections director, said legal questions about voting by mail this fall could have a significant effect on budget-strained local governments if they’re forced to order new envelopes that meet a different federal standard.

“It’s a huge issue,” he said. “It’s not just the logistical challenges of implementing this. It’s the tax dollars that would be wasted to throw all these envelopes away.”

A coalition of Democratic-led states and Washington, D.C. challenged the new rule as unconstitutional. But on Monday, the Supreme Court said that move was premature because the voting rules had yet to take hold and their effect on states was unclear. “On that score, time will tell,” the court’s conservative majority wrote.

The Postal Service’s final rule explained how it would carry out the executive order, a move that opens the door to new lawsuits. The Supreme Court allowed for that possibility in its order, writing that “if the Postal Service’s final rule harms the states, they may challenge that rule.”

In an interview, Jena Griswold, Colorado’s secretary of state, said she was disappointed by the Supreme Court’s decision, but stressed — like top election officials in other states — that multiple legal avenues remained.

“The Supreme Court did not answer the question: Is this executive order unlawful?” she said. “They only answered the question, did the lower courts weigh in too soon on this?”

In Utah, Lt. Gov. Deidre Henderson, the state’s top election official, has been critical of the Trump administration’s efforts to tighten voting rules. Ms. Henderson, a Republican, said in a statement: “I assure all Utah voters that they will be defended. We will run a secure election in accordance with state and federal law.”

Democrats and voting rights groups have argued that the executive order violated the Constitution because Congress and the states have authority over elections, not the president.

California and other Democratic-led states have also moved to shore up existing laws, including some signed this year, aimed at toughening election protections around who can have access to key voting data and speeding up the counting process for mail votes.

President Trump has repeatedly said that mail-in voting is “cheating,” “corrupt” and “horrible,” despite having voted by mail as recently as this month in Florida’s Republican primary. He has moved to restrict mail-in voting using a variety of procedural and legislative levers, though many of those efforts have failed to overcome judicial scrutiny or resistance from within his own party.

Even as some Republicans have started encouraging their voters to use mail-in ballots, several G.O.P. state leaders have broadly sided with the president’s claims of election fraud. Attorney General Liz Murrill of Louisiana, for example, called Monday’s ruling a “huge win for election integrity.”

Some election experts have also warned that, regardless of whether the changes are enacted, Mr. Trump’s baseless claims against mail-in voting will continue to undermine faith in the security of American elections.

Aaron Blacksberg, federal policy counsel at the Institute for Responsive Government, a policy think tank, said that while the court’s ruling did not change anything, practically, “the confusion and chaos does matter.”

“It’s hard for even the legal wonks to follow,” he said.

Nick Corasaniti contributed reporting from New York and Laurel Rosenhall from Sacramento.