The federal government's pressure on lenders Wednesday to fix the paperwork problems plaguing foreclosures left unaddressed a far greater potential threat facing the financial system and the U.S. economy.

Beyond sloppy documents, the foreclosure debacle has exposed one of Wall Street's little-known practices: For more than a decade, big lenders sold millions of mortgages around the globe at lightning speed without properly transferring the physical documents that prove who legally owned the loans.

Now, some of the pension systems, hedge funds and other investors that took big losses on the loans are seeking to use this flaw to force banks to compensate them or even invalidate the mortgage trades themselves.

Their collective actions, if successful, could blow a hole through the balance sheets of big banks and raise fundamental questions about the financial system, financial analysts and a lawmaker said.

If judges rule in favor of such lawsuits, "it could be 2008 all over again," said Josh Rosner, managing director at Graham Fisher & Co., referring to the Wall Street meltdown that occurred after Lehman Brothers collapsed.

Financial and legal analysts are divided over how the ownership questions will be resolved and the scope of the potential damage. Lenders and investigators are in the midst of a painstaking process of unraveling the complex chain of loans that were sold from one party to another, a process that some analysts say could take years.

Of the nearly $11 trillion in mortgages in the United States, about two-thirds was turned into securities that were traded around the globe.

After a home buyer gets a mortgage, the lender typically pools that loan with hundreds of others to create a security that can be traded like a stock. This process is commonly called securitization and has been the preferred method of financing debt in America for more than a decade.

Wall Street firms would set up partnerships called "trusts" and would raise money from pension funds, university endowments, hedge funds and other investors to buy these mortgage securities. The investors would then share the cash flow from the payments made by homeowners every month.

However, local laws in most states dictate that each time a mortgage changes hands, the transaction needs to be recorded in courts or county offices. But the speed with which the loans were being generated during the housing boom and then pooled together and passed around Wall Street meant that big financial firms took shortcuts, consumer lawyers said.

Often the proper paperwork got lost or was passed along without being filled out, lawyers say. Some documents have been found retroactively signed or even forged.

"It now appears that in many cases: 1. the paperwork was not properly transferred and 2. it is unclear in many cases where the actual paperwork actually rests today," Citigroup Global Markets analyst Josh Levin wrote in a note to investors this week.