The problem here is the use of terminology which means different things to different people. To me - following the Austrian school - inflation and deflation are monetary phenomena. If the money supply is increasing, we have inflation and if it decreasing then we have deflation. By this definition it is not possible to have both at once.

What you are describing is the movement of prices, which often follow changes in the money supply, but not always if other factors are at play. If the money supply were suddenly doubled while all else stayed the same, you would expect prices to double eventually as well, but all else does not necessarily stay the same.

For instance, increases in the M3 of some 13% per year in recent years have not ignited a wage/price spiral due to global competition keeping a lid on both wages and the prices of manufactured goods. Wages have stagnated, while cheap plastic tat from China has fallen in price. Stagnating wages set against a backdrop of rising monetary inflation means that wages are falling in real terms. Falling prices for manufactured goods against the same backdrop mean that prices have been crashing in real terms.

Similarly, prices can rise against a backdrop a falling money supply, which means they would be going through the roof in real terms. This could well happen to oil and food after an initial price collapse, as there are many circumnstances that could hit supply as hard as deflation will hit demand. You could indeed see food and energy prices rise while asset prices continue to fall, but calling it inflation and deflation confuses the issue.

ShadowStats says M3 is approaching 16% and seems to be accelerating. Yet it seems like deflation ought to already be happening and measurable, given the freeze up of the various securities related to real estate mortgages in the States. Is this simply being compensated (and then some) by adding money and/or credit elsewhere? How does this work, what is M3 and when and how does it end?

M3 is a measure of broad money, but not broad enough to capture the full scope of the credit expanion we've seen in recent years (derivatives and all). The money supply in broadest terms has effectively been increasing far faster than M3 would suggest.

In other words, M3 is only part way up the inverted pyramid of credit. The credit contraction we've seen this year has not proceeded down to that level yet. I would argue that it will in the new year, whereupon credit contraction will become much more noticeable to ordinary people, in terms of their personal access to credit being curtailed.

Is this 'broader' money supply the $80T number I have seen a few times that presumably refers to the products of mainly hedge funds that lever relatively small pools of, say, mortgages into mortgage backed securities? And, if so, is it safe to say that this broad supply of credit is officially deflating or is it just not inflating as quickly as it was before?

well, the derivatives market is currently valued at $516 trillion by the Bank of International Settlements (the central bankers' central bank). Most of that was money pulled out of thin air, and destined to return to where it came from IMO. I would say by the broadest definition of money supply, we are already seeing deflation. As it works its way down the inverted pyramid, it will rapidly become more apparent.

Gotcha. Austrian terminology it is.
itulip.com refers to this as ka-poom theory:
A rapid deflation caused by a credit crunch followed by frenzied inflation as central banks attempt to prop up asset prices.
Though I suppose that's just a cute name for a crack-up boom.