FRANKFURT - Big European banks may be required to raise billions of euros in new capital, making them less risky but potentially putting them at a disadvantage to their American rivals, under guidelines issued Wednesday by an organization that coordinates global bank regulation.
The Basel Committee on Banking Supervision, which includes regulators from the United States, Europe, Japan and other major economies, issued a revised proposal Wednesday on how banks should calculate their so-called leverage ratios, a measure of how much of other people's money lenders use to conduct business.
If put into force, the new rules would probably fall hardest on large European institutions like Deutsche Bank and Barclays, which tend to use a high proportion of borrowed money to do business or have large portfolios of derivatives.
American banks have faced controls on leverage for decades, while most European banks have not. As a result, Europe's banks may have to struggle harder to comply with the new rules. ‘‘This will essentially be the first time European banks will be subject to a leverage ratio,'' said Andrew S. Fei, a lawyer in the New York office of Davis Polk who specializes in bank regulation.
While highly technical, the proposed rules are at the center of efforts to ensure that taxpayers never again have to bail out big banks amid a fina ncial crisis. Banks have lobbied intensively for rules that allowed them to risk large amounts of borrowed money, which provides them the opportunity to increase profits. But the guidelines issued Wednesday appear to reflect warnings by many economists that bank risk remains too high.
Stefan Ingves, chairman of the Basel Committee and governor of the Swedish central bank, said the rules would also eliminate discrepancies in the way leverage was calculated in different countries.
‘‘This ensures investors and other stakeholders will have a comparable measure of bank leverage, regardless of domestic accounting standards,'' Mr. Ingves said in a statement.
The proposed guidelines come amid signs that, elsewhere in Europe, the political will to rein in bank risk is flagging. Euro-zone finance ministers met in Brussels on Wednesday in yet another effort to reach an agreement on a so-called banking union, in which countries would share some of the cost of recap italizing banks.
Marathon talks on the subject last week ended in deadlock. The ministers were not expected to conclude the latest round of talks until late Wednesday or early Thursday, and it was uncertain whether they would be able to reach an agreement.
The new rules from the Basel Committee are not binding on individual countries and would not take full effect until the beginning of 2018. Banks and other interested parties have until Sept. 20 to comment on the guidelines, which could be further revised before the committee votes on the proposal.
Banks that are short of capital under the new guidelines could face market pressure to raise money well before the rules take effect. That is because, beginning in 2015, the banks would be required to disclose much more information about what kind of risk they carry on their books.
Some governments, anxious to avoid asking taxpayers to rescue banks again, have already been compelling lenders to raise more capital. The Prudential Regulatory Authority in Britain ordered Barclays last week to submit a plan by the end of the month on how the institution would increase capital and reduce leverage.
The Bank of England warned on Wednesday that banks might need to further bolster their capital because of big swings in asset prices that had taken place in recent weeks, as markets reacted to signs that the Federal Reserve in the United States was likely to scale back its stimulus measures.
‘‘Authorities need to be alert to whether stability could be threatened by excessive leverage o r liquidity risk building up in any potentially vulnerable parts of the financial system,'' said Paul Tucker, deputy governor for financial stability at the British central bank. ‘‘That has been underlined by the abrupt correction in asset prices over recent weeks.''
Rules on leverage have been the subject of an intense, behind-the-scenes debate between bankers and regulators for several years, as well as a source of tension between the United States and Europe.
German and French regulators have pushed for rules that give banks wide discretion to estimate their risk from loans, derivatives or other assets. But American regulators, along with many economists, have argued that banks cannot be relied on to judge risk accurately.
Thomas M. Hoenig, vice chairman of the Federal Deposit Insurance Corporation, told an audience in Basel in April that measures of risk based on banks' own calculations created ‘‘the illusion that these firms are well capitalized.''
In 2010, the Basel Committee proposed a leverage ratio of 3 percent, meaning that banks would need to hold about $1 in capital for every $33 in risk or other financial exposure. But there remained questions about how banks should be required to value their portfolios and calculate the ratio.
While European banks would tend to be hit hardest by the new rules, American banks could also feel pressure. Some of the methods they use to discount derivatives exposure under American accounting rules would no longer be allowed. Higher exposure would increase their need for capital.
Even with the stricter guidelines proposed Wednesday, economists expressed concern that banks were continuing to operate with thin capital cushions.
‘‘We are still looking at very low numbers from a historical perspective,'' said Harald Benink, a professor of banking and finance at Tilburg University in the Netherlands. ‘‘If we really want to protect the taxpayers, we need to start looking at numbers that are more ambitious.''
