When will Moody's press the button? When Moody's are thinking of a downgrade, you know that it has already happened.

Feb. 4 (Bloomberg) -- Moody's Investors Service may cut the ratings on A$83 billion ($75 billion) of Australian mortgage- backed bonds linked to PMI Group Inc. on concern the U.S. home- loan insurer will find it harder to pay claims.

Moody's is reviewing the ratings on bonds tied to loans insured by the local unit of PMI, it said today in a statement. They account for about 45 percent of the A$180 billion mortgage- backed bonds issued in Australia, making for the biggest review Moody's has done in the nation, said Henry Charpentier, structured finance analyst at the ratings company in Sydney.

Any downgrades will stifle sales of Australian mortgage- backed bonds, which fell 87 percent in the six months to Dec. 31. Australian lenders will find it more costly to raise capital to fund mortgages if Moody's cuts the ratings.