The Standard & Poor’s 500-stock index fell 2 percent in the morning, then rebounded partly in reaction to a report that said banks were nearing the end of subprime mortgage losses. It was up nearly 1 percent in the afternoon before paring that gain to close up 0.5 percent, to 1,315.48 points. The Dow Jones industrial average closed up 35.5 points, to 12,145.74 points.

Image The Tokyo foreign exchange market. Credit... Shizuo Kambayashi/Associated Press

A toxic blend of economic and financial developments is testing policy makers and lawmakers who are struggling to contain the slump brought on by the collapse of the mortgage market, a downturn that now looks sure to push the economy into a recession. Though current conditions are a far cry from the 1970s, resurgent inflation is raising the threat of stagflation  a condition in which unemployment and the price of goods and services both rise.

Since the credit markets began to seize up in August, the steps taken by the Federal Reserve and the rest of the federal government have often bolstered stocks briefly, but so far they have done little to stem the larger downward drift.

Many specialists say policy makers can do only so much to protect the economy and warn that the government should be careful not to exacerbate inflation and create a new bubble like the one in housing that has burst. Lower interest rates and increased federal spending may not be enough to shore up growth, and some suggest that the only remedy for the pain may be the pain itself. A Standard & Poor’s report predicted that subprime mortgage write-downs at banks were nearly done, though losses in other areas might continue.

“We have to be careful about what medicines we throw at this, whether it’s stimulus packages or a bailout,” said Liz Ann Sonders, chief investment strategist at Charles Schwab & Company. “A lot of what we are dealing with is a solvency problem. We need to let the system wash it out.”