The Treasury's number two official vowed on Thursday to fight efforts to weaken the U.S. financial reform bill and said it should include the so-called Volcker rule which would separate banking from proprietary trading.

Deputy Treasury Secretary Neal Wolin also said U.S. Senate and House of Representatives conferees working to reconcile their versions of the bill should also oppose efforts to weaken a new consumer financial protection agency with more lenient lending rules for car dealers.

As conferees begin the process of reconciling the remaining differences in the two bills, we will continue to fight for the strongest financial reform bill possible, Wolin said in a speech to the Financial Industry Regulatory Authority's annual conference here.

And we will oppose any attempts by particular interests to use the conference process as an opportunity to weaken the final bill, he added.

Wolin's remarks did not directly address the Obama administration's view of a controversial plan to force banks to spin off their swaps trading desks to reduce risks in the financial system. Another Treasury official, assistant secretary Michael Barr on Wednesday said this was not a core provision and was subject to alterations.

But the deputy secretary praised the derivatives provisions in both the House and Senate bills, saying they would provide for strong regulation and transparency for all derivatives.

He said the administration would work hard to include the Volcker rule provisions, which are aimed at reducing risks by prohibiting depository banks from trading for their own accounts. These also would limit the size of financial firms by limiting mergers that concentrate more than 10 percent of financial system liabilities into a single company.

He said the Obama administration -- which owns nearly 61 percent of General Motors Co and nearly 10 percent of Chrysler, does not want to interfere with car dealers' ability to sell cars by subjecting them to tougher consumer protection rules.

But where car dealers act like banks or like other non-bank financial companies, they should be subject to the same consistent rules of the road, he added.

(Reporting by Joseph Giannone and David Lawder, writing by David Lawder, Editing by Andrew Hay)