Sen. Maria Cantwell, D-Wash., has blocked three nominations to the Commodity Futures Trading Commission, saying the agency has failed to regulate oil markets.

“They’ve dropped the ball,” she said Thursday. “The consequences are the American people are paying hand over fist for our inability to rein in oil traders and properly do oversight.”

Cantwell, who has criticized the commission for months and urged tougher regulation of oil and gas markets, said she will keep an indefinite block on the nominations of the acting chairman, Walter Lukken, and two other nominees. The CFTC has five commissioners. Under Senate rules, a single lawmaker can block a nomination or legislation by issuing a “hold,” or block.

“It’s not something I do routinely,” Cantwell said. “But the public needs to know they are doing nothing and I am tired of prodding them.”

In speech on the Senate floor Thursday, Cantwell said the CFTC and the Bush administration were “watching out more for Wall street than Main Street. We need transparency and tough rules in place to make sure that markets work for the consumer.”

Cantwell’s action comes as the Senate moves ahead with a Democratic plan to curb speculation in oil markets that has been blamed for some of the recent run-up in oil prices. Democrats say the price increases are due in part to speculation and investment by Wall Street traders who are buying huge quantities of oil just to resell at a higher price.

Cantwell said she was encouraged that the CFTC charged an oil trading company Thursday with manipulating oil prices _ the first indictment to come down since the regulators began a new investigation into wrongdoing in the energy markets. Netherlands-based Optiver Holding, two of its subsidiaries and three employees were charged with manipulation and attempted manipulation of crude oil, heating oil and gasoline futures on the New York Mercantile Exchange.

An agency spokesman declined comment.

The White House said that CFTC investigations had resulted in 58 enforcement actions against 157 defendants in the last year. Proceedings initiated by the CFTC have yielded more than $133 million in civil penalties and $105 million in restitution, the White House said in a statement.

Besides Lukken, who has served on the CFTC since 2002 and has been nominated as chairman, Cantwell also is blocking the nominations of commissioner Bart Chilton to a new term and Scott O’Malia, a new appointee. Chilton is a former Clinton administration official and leader of the National Farm Union. O’Malia is a former aide to GOP Sens. Mitch McConnell of Kentucky and Pete Domenici of New Mexico.

The Senate energy bill moved forward this week on a procedural vote, but has since bogged down amid partisan squabbling.