By Phil Wahba

NEW YORK (Reuters) - Microsoft founder Bill Gates is the richest person in the United States for the 15th year in a row, but economic woes have claimed some members of Forbes magazine ranking of the 400 wealthiest Americans.

Dropouts this year include former American International Group chief executive Maurice Greenberg, and former eBay chief Meg Whitman, while among those on the list some 126 fortunes declined -- six times more than last year.

Casino magnate Sheldon Adelson saw his fortune dwindle by $13 billion in the past year, the biggest loss of anyone on the list, while Kirk Kerkorian's fortune shrank by $6.8 billion as shares in casino operator MGM Mirage tumbled.

"The fact that the rich are not getting richer means that the economy is locked," said Matthew Miller, editor of the Forbes list. "Credit is not being extended, there is very little liquidity in the markets and deals can't get done, so the economy contracts."