How’s this for a merry little Christmas?

Before the U.S. holiday shopping season even begins, Morgan Stanley’s chief U.S. economist has given up on consumer spending — not only through Christmas ‘08 but all the way until next summer at the earliest.

“As we see it, the current collapse in consumer spending likely will be the most severe and longest in the postwar (World War Two) period,” economist Richard Berner wrote in a note to clients. ”The recovery in consumer spending likely will be moderate as consumers embark on a long period of rebuilding thrift.

Why so grim? Well, between the 1.2 million jobs lost since the beginning of the year and the downdraft in the housing and stock markets, income is taking a hit and household wealth is down about $7 trillion. Yes, trillion with a ‘T.’ Oh yeah, and there’s that credit crunch.

Berner calls this the “perfect consumer storm” and says it will rage until mid-2009.

Now that you’re thoroughly depressed, we should mention the silver lining. The drop in gasoline prices to $2.45 per gallon from $4 represents $225 billion in consumers’ pockets. Add in another round of fiscal stimulus and it should limit — though not offset — the other strains on the system.

“Done right, and coupled with other policies to mitigate the credit crunch and foreclosures, these steps should promote a modest recovery beginning in 2010,” Berner said.