Moody’s Investors Service and Standard & Poor’s, reeling from criticism over the way they rated asset- backed debt, face tougher global regulation to prevent a repeat of the American subprime mortgage crisis.

The International Organization of Securities Commissions, the forum for more than 100 regulators, said ratings firms will be banned from recommending how products are structured to help prevent conflicts of interest, and called for independent reviews of the way rankings are assigned. The companies should create new ratings to differentiate structured bonds from corporate securities, Madrid-based IOSCO said yesterday.

The chairman of the U.S. Securities and Exchange Commission, Christopher Cox, and European regulators have rebuked Moody’s, S&P, and Fitch Ratings, all based in New York, for giving top rankings to mortgage securities that contributed to $383 billion of writedowns and losses triggered by the subprime slump. The 27-nation European Union also may consider requiring rating companies to register with authorities, French Finance Minister Christine Lagarde said yesterday. New SEC rules are scheduled to be published June 11, Mr. Cox said.

“They will be sturdy rules based on the lessons learned in the subprime experience,” Mr. Cox said in an interview at IOSCO’s annual meeting in Paris.

Moody’s Corp., parent of the ratings company, rose $1.33, or 3.8%, to $36.20 in New York Stock Exchange composite trading after the IOSCO announcement fell short of regulation that would dictate the company’s fees or assert other forms of control. S&P parent McGraw-Hill Cos. fell 16 cents to $39.69.

Investors “realize that nothing is going to happen” that would hurt the stock, a managing director at investment research firm Graham Fisher & Co. in New York and co-author of a study last year that said ratings companies understate the risks of subprime mortgage bonds, Joshua Rosner, said.

IOSCO has no direct regulatory power, working instead through its members, which include the SEC and the U.K.’s Financial Services Authority.

IOSCO first drafted a credit ratings code in 2004 in response to the ratings companies’ failure to act before the bankruptcies of formerly investment-grade issuers such as Enron Corp.

The SEC’s rules will require greater disclosure so that regulators can “test the quality of the analysis,” Mr. Cox said.

“We’re going to prohibit the kinds of practices that were found to be particularly troublesome in the subprime crisis, so conflicts of interest will either be flat-out prohibited or subjected to procedures to minimize those conflicts,” Mr. Cox said.

The SEC has been probing whether ratings companies were pressured to give top rankings to securities by issuers who paid for the ratings.

Ms. Lagarde plans to raise the idea of registering the ratings firms at a meeting of her counterparts in July, she said in a speech to the IOSCO conference yesterday.

“It will facilitate a monitoring mechanism,” Ms. Lagarde said of registration, which she said would also match the situation in America and some other countries.

Under the new code, ratings companies will be required to “differentiate ratings of structured finance products from other ratings, preferably through different rating symbols,” IOSCO said in the statement on the new code.

Moody’s and S&P are reviewing the IOSCO’s code and examining ways to implement it, spokespeople for the companies said.

Fitch will shortly issue a consultation paper seeking comment on “potential additional and complementary rating scales for structured finance securities,” the president of Fitch Ratings, Stephen Joynt, said in an e-mailed statement.

Regulators have trailed behind some investor opinions on structured finance for the past year. The manager of the world’s biggest bond fund, Bill Gross, said 11 months ago that ratings companies were duped into giving top credit ratings on some structured transactions and warned bondholders could lose all their money.