A Republican legislative proposal would make it harder for the Securities and Exchange Commission to do its job of policing and regulating the financial markets, the chairman of the agency argues in testimony prepared for delivery Thursday.

The House bill calls for the SEC to weigh a variety of factors before issuing regulations, including, potentially, whether the rules are tailored “to impose the least burden on society.”

The term “society” includes “businesses of differing sizes,” the bill says.

The bill, by Rep. Scott Garrett (R-N.J.) and other members of the House Financial Services Committee, guides the SEC to assess “the best way of protecting” both the public and “market participants.”

That language could conflict with the SEC’s mission, SEC Chairman Mary L. Schapiro says in written testimony.

“The SEC’s mission is to protect investors, which in some cases means protecting them from certain market participants,” Schapiro says.

The bill, called the “The SEC Regulatory Accountability Act,” would require the SEC to issue orders only if it first determines that the benefits justify the costs.

That could undermine the SEC’s ability to take enforcement action against wrongdoers, Schapiro says.

The bill tempers its language about imposing the least burden on society by saying the SEC analysis should be “consistent with . . . regulatory objectives.”

The SEC is responsible for regulating the stock markets and making sure publicly traded companies don’t deceive investors about their financial performance. The agency polices such offenses as insider trading and accounting fraud.

In what is largely a partisan battle, Democrats have responded to the financial crisis by pushing to expand the agency’s responsibilities, while many Republicans and businesses have opposed the regulatory expansion.

The hearing Thursday by the Financial Services Committee is also slated to examine a plan by committee chairman Spencer Bachus to restructure the SEC.

Bachus has said the bill would modernize the SEC. Arthur Levitt Jr., who headed the SEC during the Clinton administration, has said it would eviscerate the agency.