In a move that highlights the difficulty of regulating ratings agencies, Standard & Poor’s has joined Moody’s in withdrawing its application to supply ratings of corporate bonds and other debt-based securities to retail investors in Australia, after new rules were announced this month by the Australian Securities and Investments Commission.

The rules, which will take effect Jan. 1, are intended to improve the management of risk and conflicts of interest at the ratings agencies, as well as increase transparency. But a clause that requires them to resolve disputes with retail investors through a financial ombudsman is one reason S.&P. is citing for withdrawing from the market, where it is among the three major agencies, alongside Moody’s and Fitch.

“Because the local ombudsman would effectively be second-guessing S.&P.’s analysts, we believe this would ultimately create investor confusion and harm financial markets,” John Bailey, managing director of S.&P. in Australia and New Zealand, said in a statement Wednesday.

The retail bond market in Australia is not as large as the wholesale market of institutional investors, for which S.&P. is still applying for a license. It is unlikely S&P would cut jobs as a result of its decision to leave the retail market.

“This scheme could change the substance of a rating and result in the creation of dual credit ratings — an Australian ‘EDR’ domestic credit rating and a ‘rest of the world’ credit rating,” Mr. Bailey said, referring to the external dispute resolution of the ombudsman.

S.&P. said in a separate statement Thursday that, while it was withdrawing from the retail credit-rating market, its services to rate funds for retail investors based on how they manage assets would still be available.

Currently, ratings agencies in Australia are not forced to resolve disputes through an ombudsman for the credit ratings they provide investors. The new rules, in line with a global push to improve the reliability of debt ratings that played a crucial role in the financial crisis, aim to make the agencies more accountable.

“Dependent as they were on the banks for their revenue, the agencies were hopelessly conflicted by the lure of big profits in return for easy ratings,” Kevin Rudd, the Australian prime minister, wrote in an analysis of the financial crisis, published in February.

Without ratings available to investors, it may be more difficult for companies to convince people to buy bonds and other debt instruments in Australia, and force them to borrow in markets abroad. In the first 10 months of 2009, corporate debt issuance in the country, including retail, came to 2.4 billion Australian dollars, or $2.2 billion.

While Fitch Ratings said this month that it had applied for a retail credit-ratings license, it is not clear whether it will press forward with it, which would leave Australia only with local debt-rating agencies.

The decision by Moody’s and S.&P. to curtail their operations in Australia highlights the larger issue of how far governments can push to strengthen regulations before ratings agencies and others simply walk away, while continuing to operate in more lenient jurisdictions. A similar situation is brewing in Britain, which faces European Union regulations that threaten to put new limit hedge funds, even as Switzerland — which is not an E.U. member — woos them with less onerous laws.

In the United States, the Securities and Exchange Commission voted in September to increase oversight on the ratings agencies by adopting and proposing measures to assure greater transparency and competition and to manage conflicts of interest.

“These proposals are needed because investors often consider ratings when evaluating whether to purchase or sell a particular security,” Mary Schapiro, the commission’s chairperson, said at the time. “That reliance did not serve them well over the last several years.”

– Chris V. Nicholson