Though credit ratings may be crunched, the Federal Reserve’s credibility should remain platinum.

The national bank – despite growing crises in world markets – cannot deviate from putting the needs of every American first, not just those of investors who might lose their shirts.

Some have criticized the Fed as lagging, with its seemingly timid response to the subprime mortgage meltdown – cutting the discount lending rate to banks by a half-percent, regarded as an emergency measure designed to stabilize the market. Some in the industry, and government, believe it should do more.

It has put Ben Bernanke, the Fed chairman, in the untenable position of fending off political and market pressure to preserve the Fed’s autonomy over economic policy. He must succeed, as the Fed should act carefully on factual assessments of economic indicators, not as the guardian angel for the missteps of capitalists or Capitol Hill.

So far, Bernanke is showing his savvy. The Fed isn’t a safety net, especially for overindulgent investors or lenders now realizing the cheap credit of the past came with a cost: U.S. currency is about to become much more expensive.

Maine, this year, joined several other states in enacting legislation to curb predatory subprime mortgage lenders, who capitalized on plentiful credit and low interest rates to ensnare vulnerable borrowers, many of whom couldn’t afford the lender’s terms to begin with. Built upon this fallacy, subprime lenders are now collapsing.

So are private equity pirates, who built empires on the subprime principle: with a low down payment and near-infinite credit, everything from half of midtown Manhattan to the Chrysler Corp. could be yours.

Just sign on the dotted line.

These risky and ambitious practices created this current tailspin. In the ongoing post-mortem, experts are unearthing blame in every corner: aggressive Fed policies under former Chairman Alan Greenspan, those unsavory mortgage lenders, and the appetite of venture capitalists to acquire on margin, and sell for the same.

For the market, it’s execution by firing squad: though one shot might be fatal, all the shooters share culpability.

Usually, those put against the wall are there from their own making. Clemency can come from a higher power, as long as it serves the broad interest of justice. In this market, the Fed is the governor with a hand on telephone, weighing whether to make the call. It has the discretion to do so.

But not, it must be remembered, any obligation.