Finally, a Wall Street conspiracy theory without Goldman Sachs at its heart. This one posits that bond rater Moody’s wants to ding the U.S. credit rating so panicky politicos will privatize Social Security. That would sent big bucks to the firm’s big bank clients. If only it were true.

This bit of speculation comes from Dean Baker, a respected Washington think-tank economist, albeit with a liberal bent. Baker suggests that Moody’s increased debt warning of late “could be a reflection of the Wall Street agenda to cut” America’s social insurance safety net. Shifting government pensions into the private sector could entail billions, if not trillions, of retirement dollars flowing into personal portfolios managed by investment firms.

Like most conspiracy theories, this one reveals more about the storyteller than about reality. Baker, like other left-of-center economists such as New York Times columnist Paul Krugman, think Washington too concerned with deficits given the anemic economy. And they lump President Barack Obama into that camp, too. They fret this New Frugality — somewhat laughable give trillion dollar deficits — will be further fed by Obama’s new deficit commission. And they especially worry the panel will recommend trimming back Social Security to preserve its solvency. Add in displeasure that financial reform isn’t tougher on the major players in the financial meltdown, and a juicy tale of corporate collusion emerges.

A better theory: Raters have been intentionally insouciant so as not to incur the wrath of Congress as it fashions new regulations for the firms. U.S. debt-to-GDP may hit 90 percent by 2020, according to the Congressional Budget Office. The CBO also says that Social Security, which accounts for 16 percent of the government’s $46 trillion in long-term liabilities, will in 2010 for the first time pay out more in benefits it takes in from taxes. ┬áThat is six year earlier than predicted. The slow economy is the near-term cause. But the event marks a key milestone in the program’s long descent toward insolvency. Benefit cuts and tax hikes seem inevitable. But those will lower an already paltry rate of return, especially for younger workers.

Letting Americans shift at least some of their government-directed savings into the real economy would generate a bigger nest egg. ┬áThis is done in Chile and Sweden, for instance. Yes, stocks are risky. But the market ultimately reflect the real economy. If it booms, so will portfolios. And if doesn’t, Social Security is in even deeper trouble. If there isn’t a conspiracy, someone should hatch one.