NEW YORK — The equity Americans have in their most important asset — their homes — has dropped to its lowest level since the end of World War II.

Homeowners' portion of equity slipped to 46.2 percent in the first quarter from a revised 47.5 percent in the prior quarter. That was the fifth straight quarter below the 50 percent mark, the Federal Reserve said yesterday.

The total dollar value of equity also fell for the fourth consecutive quarter to $9.12 trillion from $9.52 trillion in the fourth quarter, while Americans' total mortgage debt rose to $10.6 trillion from $10.53 trillion.

A homeowner's equity is the market value of a property minus the mortgage debt.

Experts expect equity to decline further, dragging more homeowners "upside down" on their mortgages.

At the end of March, nearly 8.5 million homeowners had negative or no equity in their homes, representing more than 16 percent of all homeowners with a mortgage, according to Moody's Economy.com Chief Economist Mark Zandi. By June 2009, he estimates that will rise to 12.2 million, or almost one out of four homeowners with a mortgage.

But to put that number in perspective, one out of every three homeowners own their properties free and clear, with no mortgage at all.