A 2011 SEC report-opposed at the time by the agency's two Republican commissioners-said consumers are often baffled by the distinction between brokers and advisors. The report recommended a uniform standard "to act in the best interest of the customer without regard to the financial or other interest of the broker, dealer, or investment advisor."

Schapiro called the change a priority and said in December that "it remains difficult to justify" two standards for the same type of advice.

In a departure from criticism of other Dodd-Frank rules, the Securities Industry and Financial Markets Association, the Wall Street trade group, supports the change.

"Sifma is very much in favor of establishing a new uniform fiduciary standard for both brokers and advisors where they're basically doing the same thing for retail customers," Ira Hammerman, Sifma's general counsel, said in an interview. "There are literally trillions of dollars of individual savings and investments that we're talking about here."

The fiduciary idea has taken "a back seat" to rules the SEC has to get done, Hammerman said, and it's "difficult to expect" the rule to be adopted this year.

Amid general agreement that investment professionals offering advisory services should act in their clients' best interests and operate under the same standards, there's division over how to implement a uniform fiduciary standard to the brokerage-industry business model, according to Steven Wallman, a former SEC commissioner and founder of online brokerage Folio Investing in McLean, Virginia.

Investment advisors generally don't support a definition that would weaken the current standard, while some Republican lawmakers oppose the rule altogether.

U.S. Representative Scott Garrett, a New Jersey Republican who leads a panel that oversees the SEC, said in a December letter to Schapiro that a hearing he held yielded a "consensus view that there is currently no evidentiary basis for proposing new standard-of-conduct regulations."

A court decision has contributed to the delay. In 2011, the U.S. Court of Appeals in Washington rejected an unrelated SEC rule, saying the agency failed to adequately assess its costs. Since then, the SEC has returned to the drawing board to bolster cost-benefit cases for many rules.

For the uniform fiduciary standard, the SEC plans to first put out a request for public comments on its potential costs. After a 60- or 90-day comment period, the agency would issue a proposal that would then also require a public-comment process and revisions before commissioners could vote. Even if started today, the typical process would extend well into 2013.