"Two different agencies with two very different approaches essentially monitor the same securities," Nasdaq CEO Robert Greifeld said at a National Press Club event in Washington.

The Securities and Exchange Commission was established after the 1929 market crash to protect investors and police securities markets. The Commodity Futures Trading Commission was born in 1974 to regulate commodity futures and options markets.

But now many securities, such as options on certain types of exchange traded funds, can fall under the jurisdiction of both regulators. Also many products such as credit default swaps, widely blamed for contributing to the global financial meltdown, have fallen through regulatory cracks.

Greifeld said it was incomprehensible that the United States has two regulators at a time when financial products have evolved into instruments that are virtually indistinguishable from one another.

Greifeld joins the growing chorus of those calling for a merger of the two agencies. Wall Street lobby group, the Securities Industry and Financial Markets Association, also supports such a merger.

The Government Accountability Office, congressional investigators, issued a report on Thursday calling for eliminating overlapping federal regulatory missions and enhancing consumer and investor protections.

This comes as Congress gets ready to reform the country's regulatory structure amid the worst financial crisis in decades.

Greifeld said there needs to be a single regulator to oversee all risk in the financial system -- an idea already put forth by the Treasury Department in March 2008 and supported by key lawmaker, Rep Barney Frank.

(Reporting by Rachelle Younglai; Editing by Bernard Orr)