The Federal Reserve's charter mandates its responsibility and first priority is to maintain the health of US Banks. It's emegergency rate cut of .75% Tuesday was not to help the stock market, but to try to RE-LIQUIFY US Banks by increasing the yield spread (between what they have to pay the Federal Reserve for loans to thenmselves, and what they pay us for our deposits and the interest they charge us on the loans they make to us). Example: They pay Fed 3.75% to get a $100,000,000 loan now that used to cost them 4.5%. They decrease the interest rates on our CD's to 2.5% and do not change credit card interest rates. Bingo, they make more money.
What's the issue? Several major US Banks are having SEVERE liquidity problems (the assets on their books, like mortgage-backed securities and Private Equity (Leveraged Buy-out) loans are now worth less, sometimes much less, in the market place than their stated book values. This type of thing can lead to insolvency.
Why an emergency rate cut? Because of SEVERE problems with what are called monoline insurers, like MBIA and Ambac. During Housing (Real Estate)and Private Equity (PE) bubble, Wall Street Banks sold bonds to pensions funds, foreign banks, smaller US banks, etc. called asset-backed securities whose collateral was the Real Estate or corporation recently taken private. Since many buyers require AAA ratings on bonds they buy, Wall Street Banks bought what is called a credit default swap (CDS), which is really just a fancy word for insurance. MBIA and Ambac "lent" their AAA rating to bonds, and promised to pay "insurance settlement" on the bonds ("asset backed securities") if any of these bonds went bad.
Well, a lot of "asset-backed securities" or bonds are going bad and failing, MBIA and Ambac don't have the capital base to pay up, and in fact are in serious danger of losing ther AAA rating. If they lose that AAA rating, by law, things like Money Market Funds and Pensions Funds can no longer hold the bonds MBIA and Ambac are "insuring", and would be forced by law to sell them. THAT WOULD CREATE CHAOS IN THE BOND MARKETPLACE AND IN SOME CASES INSOLVENCY FOR SELECT BIG AND small BANKS.
You are talking about a serious banking crises that the Fed is trying to prevent. Also remember that the bond market is much bigger than the stock market and major problems there could sink the "real economy".
Some good, more detailed discussions on this at
http://www.nakedcapitalism.com/, http://calculatedrisk.blogspot.com/, http://www.2000wave.com/article.asp?id=mwo012508