Accounting chief says last chance for global system

* No global system without United States, Tweedie says

* SEC officials say they expect a decision by 2011

* Largest companies moving to common standard

NEW YORK, Oct 28 (Reuters) - Efforts to create a single global accounting system will be set back a generation if they do not succeed within 12 to 15 months, the chairman of a global accounting rule-setting board said on Thursday.

“This is our last chance really,” said Sir David Tweedie, chairman of the International Accounting Standards Board, which sets accounting rules used in over 100 countries.

“The next year is critical, this is it,” he told a New York Society of Security Analysts conference. “We can’t kick this tin down the road much longer.”

Major economies including Japan, Canada and South Korea are joining Europe and other countries that already use accounting rules set by the IASB, but achieving a global standard could fail if the United States resists joining, Tweedie said.

The United States still uses Generally Accepted Accounting Principles (GAAP), and has been working with IASB to align its rules with international standards.

The U.S. Securities and Exchange Commission, is waiting for that convergence project to be completed before deciding whether to incorporate the international standards.

SEC officials have said they expect a decision by 2011, the same year Tweedie retires as IASB chairman.

If the SEC decides against joining, or delays its decision, political pressure on the IASB would mount, Tweedie said.

There is already “silent pressure” to remove U.S. members from the IASB because the country still uses GAAP.

“We can have international standards without the U.S.; we cannot have global standards without the U.S,” said Tweedie.

Last year, 190 of the Fortune Global 500 companies used accounting rules set by IASB, known as International Financial Reporting Standards.

More have said they plan to do so, and Tweedie said he expects the number to rise to to 245 by 2013.

But if the United States resists, other countries may decide to keep their own standards as well, thwarting the creation of a global system, Tweedie said.

U.S. policymakers generally agree that there should be one set of global accounting standards, though there is debate over how to achieve that goal.

Some critics have said a U.S. move to IFRS could jeopardize more than a century of progress under the country’s own accounting rules, which are viewed as more prescriptive.

Reporting by Dena Aubin; Editing by Ted Kerr