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The study, by Spectrem Group, the Chicago-based wealth-research firm, found that households with a net worth of $1 million or more say their assets have declined 30% or more. Nearly one-fifth of millionaires have experienced declines of more than 40%.

Nearly all the millionaires surveyed (90%) fear a prolonged economic downturn. Altogether, they believe it will last for another 22 months, and more than half (55%) are concerned they will not have sufficient assets to maintain their present lifestyles.

“The current financial crisis has had a dramatic impact on America?s millionaires, reducing their net worth substantially and threatening their ability to maintain both lifestyles and retirement plans,” said Catherine S. McBreen, Managing Director of Spectrem Group.

Spectrem?s measure of household assets doesn?t include primary real-estate but does include other real-estate, which has dropped precipitously. But for the households in Middle and Upper Richistan, where houses account for a smaller share of net worth, investment losses have been the main wealth killer. In keeping with my theme of the rich-investor revolt, many of the wealthy are blaming their wealth advisers.

According to the Spectrem study, just 36% of millionaires feel their adviser performed well during the crisis and only 14% say they will increase their use of financial advisers in the future.