Moe Tkacik | April 9, 2009, 5:14PM

Credit rating agencies are coming under fire from Congress again -- but this time it's for being too pessimistic. After Moody's issued an unprecedented across-the-board negative credit outlook on all American cities and towns yesterday, House Financial Services Committee Chairman Barney Frank issued his own negative assessment of Moody's, and scheduled a hearing to investigate:

I am troubled by the action of Moody's Investors Service to issue a negative outlook across the board on America's municipalities, which could raise the interest rates on cities and towns making it more expensive to borrow funds for infrastructure improvements.

On the face of it, this seems like a perverse round of messenger shooting. But last March, as cities and towns across the country started getting flooded with demands for huge payouts rooted in arcane details of "swap" contracts they'd inked with banks that managed their bond offerings, Frank discovered something truly perverse: the public sector was being scammed on multiple fronts by the investment banks underwriting their bond offerings -- and the profits directly fed the disastrous trade of risky mortgage-linked credit default swaps that hastened the financial meltdown.

The scheme started at the credit ratings agencies, which keep two sets of standards for grading corporate and municipal bonds -- and municipalities are held to a much higher standard, as Frank explained in a hearing using Moody's own data:

I will be giving out this chart, sectoral breakdown of Moody's rated issuers and defaulters, 1970 to 2000, general obligation bonds, there it is. Number of issuers 14,775. Number of defaults, 0.