By Tatiana Bautzer and Pete Schroeder

NEW YORK U.S. banking giants may take up to four years to set aside profits to meet new capital rules, according to a report by Morgan Stanley.

U.S. banking regulators will on Thursday unveil a sweeping proposal for stricter bank capital requirements known as the "Basel III endgame" aimed at ensuring the stability of big banks under international rules rolled out after the 2008 financial crisis.

Under the plans, the largest U.S. lenders are expected see calculations of the risk-weighted assets (RWA) they hold to rise to 20%, above an initial estimate of 12%, Morgan Stanley analysts led by Betsy Graseck wrote in a note. Holding more RWA will require banks to set aside more capital under the new standards.

Citigroup and Goldman Sachs will take three to four years to fund the higher capital requirements, the longest among the biggest U.S. lenders, Graseck estimated. Neither bank responded to requests for comment.

JPMorgan Chase and Bank of America would be able to fund the anticipated capital raises in less than two years, according to the Morgan Stanley calculations. JPMorgan declined to comment, while Bank of America did not immediately respond to requests for comment.

Most of the need to raise capital would come from assessments of the bank's operational risks and their trading books.

Morgan Stanley's predictions show a larger impact from the rules than those predicted by Federal Reserve Vice Chair Michael Barr, who said in a speech earlier this month he anticipated banks would need two years of retained earnings to catch up to the new standards.

The Federal Reserve and the Federal Deposit Insurance Corporation are expected to announce a proposal to implement the Basel III accord on Thursday, which will be followed by a public comment period.

(Reporting by Tatiana Bautzer in New York and Pete Schroeder in Washington; Editing by Lananh Nguyen and Chris Reese)