Des Moines, Iowa ? White House rivals John McCain and Barack Obama combined televised attack ads with statesmanlike appeals for bipartisanship on Tuesday as they vied for political gain in the shadow of the worst economic crisis since the Great Depression.

Both men spoke privately with President Bush about the collapse of the financial industry, then publicly made clear their differences with him, McCain more gently than his Democratic rival.

The Republican, campaigning in Iowa, pointedly told reporters there were steps the administration could still take “with the stroke of the pen to help alleviate the crisis gripping our economy. I urge them to do so.”

McCain mentioned using a federal stabilization fund to back uninsured money market accounts. The Treasury Department is already using the fund to guarantee money market mutual funds, which were the only uninsured money market accounts. Treasury announced that program Sept. 19 after the failure of Lehman Bros. produced a surge of withdrawals from such funds.

The GOP candidate also suggested wielding authority to purchase $1 trillion in mortgages. A housing bill Bush signed July 30 included

$300 billion in new loan authority for the government to back cheaper mortgages for troubled homeowners. The failed bailout bill would have added another $700 billion in authority to deal with troubled housing investments.

In addition, first Obama and then McCain said Congress should lift the current federal deposit insurance limit of $100,000 to $250,000.

Obama’s campaign released a new commercial critical of the administration and his campaign rival at the same time. “The old trickle-down theory has failed us,” the Illinois senator said in the ad. “We can’t afford four more years like the last eight.”

The intense maneuvering came one day after the House defeated a bipartisan bailout bill and the stock market responded with its largest one-day drop in history.

Those events, after 10 days of political and market uncertainty, underscored the importance of the economic debacle in a campaign with five weeks to run. Without a solution, the issue has the potential to become even more combustible in the next several days when millions of retirees and workers receive quarterly statements showing sharp drops in their personal investment accounts.

Obama has been gaining in numerous national and swing-state polls in recent days, while McCain has appeared to struggle since he announced a brief suspension in his campaign appearances to help solve the crisis.