Michael S. Barr, the Federal Reserve’s vice chair for supervision, on Monday announced that he would be pushing for significant changes to how America’s largest banks are overseen in a bid to make them more resilient in times of trouble — partly by ratcheting up how much capital they have to get them through a rough patch.

The overhaul would require the largest banks to increase their holdings of capital — cash and other readily available assets that can be used to absorb losses in times of trouble. Mr. Barr predicted that his tweaks would be “equivalent to requiring the largest banks hold an additional two percentage points of capital,” if they are implemented.

“The beauty of capital is that it doesn’t care about the source of the loss,” Mr. Barr said in his speech previewing the proposed changes. “Whatever the vulnerability or the shock, capital is able to help absorb the resulting loss.”

Mr. Barr’s proposals are not a done deal: They would need to make it through a notice-and-comment period — giving banks, lawmakers and other interested parties a chance to voice their views. If the Fed Board votes to institute them, their implementations will involve transition time. But the sweeping set of changes that he set out meaningfully tweak both how banks police their own risks and are overseen by government regulators.

“It’s definitely meaty,” said Ian Katz, an analyst at Capital Alpha who covers banking regulation.

The Fed’s vice chair for supervision, who was nominated by President Biden, has spent months reviewing capital rules for America’s largest banks, and his results have been hotly anticipated: Bank lobbyists have for months been warning about the changes he might propose. Midsize banks in particular have been outspoken, saying that any increase in regulatory requirements would be costly for them, reining in their ability to lend.

Monday’s speech made clear why banks have been worried. Mr. Barr wants to update capital requirements based on bank risk “to better reflect credit, trading and operational risk,” he said in his remarks, delivered at the Bipartisan Policy Center in Washington.

For instance, banks would no longer be able to rely on internal models to estimate some types of credit risk — the chance of losses on loans — or for particularly tough-to-predict market risks. Beyond that, banks would be required to model risks for individual trading desks for particular asset classes, instead of at the firm level.

“These changes would raise market risk capital requirements by correcting for gaps in the current rules,” Mr. Barr said.

Perhaps anticipating more bank pushback, Mr. Barr also listed existing rules that he did not plan to tighten, among them special capital requirements that apply only to the very largest banks.

The new proposal would also try to address vulnerabilities laid bare early this year, when a series of major banks collapsed.

One factor that led to the demise of Silicon Valley Bank — and sent a shock wave across the midsize banking sector — was that the bank was sitting on a pile of unrealized losses on securities classified as “available for sale.”

The lender had not been required to count those paper losses when it was calculating how much capital it needed to weather a tough period. And when it had to sell the securities to raise cash, the losses came back to bite.

Mr. Barr’s proposed adjustments would require banks with assets of $100 billion or more to account for unrealized losses and gains on such securities when calculating their regulatory capital, he said.

The changes would also toughen oversight for a wider group of large banks. Mr. Barr said that his more stringent rules would apply to firms with $100 billion or more in assets — lowering the threshold for tight oversight, which now apply the most enhanced rules to banks that are internationally active or have $700 billion or more in assets. Of the estimated 4,100 banks in the nation, roughly 30 hold $100 billion or more in assets.

Mr. Katz said that the expansion of tough rules to a wider set of banks was the most notable part of the proposal: Such a tweak was expected based on remarks from other Fed officials recently, he said, but “it’s quite a change.”

The bank blowups earlier this year illustrated that even much smaller banks have the potential to unleash chaos if they collapse.

Still, “we’re not going to know how significant these changes are until the lengthy rule-making process plays out over the next couple of years,” said Dennis Kelleher, the chief executive of the nonprofit Better Markets.

Mr. Kelleher said that in general Mr. Barr’s ideas seemed good, but added that he was troubled by what he saw as a lack of urgency among regulators.

“When it comes to bailing out the banks, they act with urgency and decisiveness, but when it comes to regulating the banks enough to prevent crashes, they’re slow and they take years.”

Bank lobbyists criticized Mr. Barr’s announcement.

“Fed Vice Chair for Supervision Barr appears to believe that the largest U.S. banks need even more capital, without providing any evidence as to why,” Kevin Fromer, the chief executive of the lobby group the Financial Services Forum, said in a statement to the news media on Monday.

“Further capital requirements on the largest U.S. banks will lead to higher borrowing costs and fewer loans for consumers and businesses — slowing our economy and impacting those on the margin hardest,” Mr. Fromer said.

Susan Wachter, a finance professor at the University of Pennsylvania’s Wharton School, said the proposed changes were “long overdue.” She said it was a relief to know that a plan to make them was underway.

The Fed vice chair hinted that additional bank oversight tweaks inspired by the March 2023 turmoil are still coming.

“I will be pursuing further changes to regulation and supervision in response to the recent banking stress,” Mr. Barr said in his speech. “I expect to have more to say on these topics in the coming months.”