Neither Congress, nor federal regulators, nor state or federal prosecutors have yet to conduct a thorough investigation into the mortgage bubble and financial bust. We welcomed the news that the Justice Department is investigating allegations that Standard & Poor’s purposely overrated toxic mortgage securities in the years before the bust. We hope the investigative circle will widen.

But a lot more needs to be done to address the continuing damage from the mortgage debacle.

Tens of millions of Americans are being crushed by the overhang of mortgage debt. And Congress and the White House have yet to figure out that the economy will not recover until housing recovers — and that won’t happen without a robust effort to curb foreclosures by modifying troubled mortgage loans.

Instead of pushing the banks to do what is needed, the Obama administration has basically urged them to do their best to help, mainly by reducing interest rates for troubled borrowers. The banks haven’t done nearly enough. In many instances, they can make more from fees and charges on defaulted loans than on modifications.

The administration needs better ideas. It can start by working with Fannie Mae and Freddie Mac, the government-run mortgage companies, to aggressively reduce the principal balances on underwater loans and to make refinancing easier for underwater borrowers. If the president championed aggressive action, and Fannie and Freddie, which back most new mortgages, also made it clear to banks that they expect principal reductions, the banks would feel considerable pressure to go along.

The housing numbers are chilling. Sales of existing homes fell in July by 3.5 percent, while prices were down 4.4 percent in July from a year earlier. In all, prices have declined 33 percent since the peak of the market five years ago, for a total loss of home equity of $6.6 trillion.

There’s no letup in sight. Currently, 14.6 million homeowners owe more on their mortgages than their homes are worth, and nearly half of them are underwater by more than 30 percent. At present, 3.5 million homes are in some stage of foreclosure. Nearly six million borrowers have already lost their homes in the bust.

Reducing principal is a better solution than lowering interest rates, because it reduces payments and restores equity. Bankers resist, because it could force them to recognize losses they would prefer to delay. The administration has resisted, in part because principal reductions are seen as rewarding reckless borrowers.

But many of today’s troubled borrowers were not reckless. Rather, they are collateral damage in a bust that has wiped out equity and hammered jobs, turning what were reasonable debt levels into unbearable burdens.

Housing advocates and bankruptcy experts are calling for the administration to try new approaches. One would have Fannie and Freddie urge banks to let underwater borrowers who file for bankruptcy apply their monthly mortgage payments to principal for five years — in effect, reducing the loan’s interest rate to zero.

Another solution would be for Fannie and Freddie to ease the rule for refinancing underwater mortgages for borrowers who are current in their payments. The lower payments on refinanced loans would help to prevent defaults and free up money for borrowers to use for paying down principal or consumer spending.

President Obama is reportedly planning to include housing relief measures in his new jobs plan. Unless the plan includes strong support for principal reductions and easier refinancings, it will not get at the root of the problem: too much mortgage debt and too little relief.