Treasury Secretary Timothy Geithner, center, talks on his mobile phone Thursday as he walks into the House Rayburn Building on Capitol Hill in Washington to appear before the House Financial Services Committee. Geithner unveiled the Obama administration’s plan to expand financial regulations, with skeptics questioning the proposal’s effectiveness.

Washington ? Tough as they seem, will the Obama administration’s strict new Wall Street rules really work?

The administration’s plan for strict scrutiny of hedge funds and other freewheeling investors, part of the biggest expansion of financial restraints since the Great Depression, is drawing opposition from Republican lawmakers and the rules’ targets. And skeptics are questioning whether they would be effective anyway.

Wall Street wizards have proved adept at designing complex financial products to sidestep existing regulations.

And Vincent Reinhart, former director of monetary affairs at the Federal Reserve, says, “You’re going to see firms try to figure out how to be under the radar.”

For example, private equity investors might try to buy large hedge funds and chop them into funds that would be small enough to operate unregulated, Reinhart said.

Treasury Secretary Timothy Geithner, unveiling the plan Thursday before the House Financial Services Committee, said the nation’s economic crisis demands bold action.

The administration’s proposals, which require congressional approval, include:

• Imposing tougher standards on financial institutions that are judged to be so big that their failure would threaten the entire system.

• Extending federal regulation for the first time to all trading in financial derivatives — exotic instruments such as credit default swaps that are blamed for much of the economic carnage.

• Requiring larger hedge funds and other private pools of capital, including private equity and venture capital funds, to register with the Securities and Exchange Commission.

• Creating a regulator to monitor the biggest institutions. Geithner did not say which agency should wield such authority, but the administration is expected to favor the Federal Reserve.

• Empowering the government to take over major nonbank financial firms such as insurers and hedge funds if deemed necessary.

Committee Chairman Barney Frank, D-Mass., and many Democrats on the panel backed the proposals, while Republicans assailed them as too far-reaching.

Private analysts also questioned whether Geithner’s plan would succeed in safeguarding the financial system.

“We’re not in this mess because we need new rules,” said Bill Fleckenstein, a Seattle-based hedge fund manager who accurately predicted the housing bubble. “We need to enforce the rules we already have.”

Timothy Brog, portfolio manager of New York-based hedge fund Locksmith Capital Management, said stricter rules won’t work properly if regulators become bogged down in policing individual funds.

“It’s not hedge funds that are a problem,” Brog said. “The problem is the instruments they are trading. A $100 million hedge fund is not going to have a material effect on the overall market.”