Nomura, Impac, Bear issued worst "Alt-As"-S&P

NEW YORK, Dec 20 (Reuters) - Nomura Holdings Inc (8604.T), Impac Mortgage Holdings Inc IMH.N and Bear Stearns Cos Inc BSC.N last year issued the worst-performing securities backed by so-called "Alt-A" mortgages, Standard & Poor's said on Thursday.

Severe delinquencies on the $4 billion in Alt-A mortgage bonds issued by Nomura hit 9.83 percent as of September, more than twice the 4.61 percent average, the report said.

Defaults for Alt-A loans -- which fall short of prime due to risky attributes such as high balances relative to property value or no proof of income -- ran as low as Citigroup Inc's (C.N) 2.27 percent due to the diversity in loan types, the rating agency said.

S&P studied the top 20 issuers of Alt-A securities responsible for 95 percent of the market. Delinquencies on Alt-A bonds issued in 2006 are more than double that of 2005, and the trend appears to be continuing for those sold this year, it said.

Poor performance of loans in U.S. mortgage bonds "at first seemed limited to the subprime mortgage sector, but has since filtered through to virtually every corner of the non-prime mortgage industry," S&P said in the report.

Alt-A delinquency rates still pale next to subprime loans. But the quality of Alt-A mortgages eroded during the housing boom as lenders loosened standards to maintain volumes.

Impac's $6.6 billion 2006 Alt-A loans are 8.31 percent delinquent, while 7.13 percent of Bear Stearns' $46.7 billion in Alt-A issuance are more than 90 days in arrears, S&P said. Morgan Stanley (MS.N) and Deutsche Bank AG (DBKGn.DE) round out the worst five, with 6.95 percent and 6.32 percent, respectively.

On Wednesday, S&P downgraded more than $7 billion in securities backed by Alt-A loans, or about 1 percent of the $694 billion rated by the company in 2005 and 2006.

For Nomura, Japan's largest brokerage, subprime loan losses resulted in the company exiting the U.S. residential mortgage market in October. Impac in September ceased nearly all its mortgage lending. Bear Stearns on Thursday reported its first quarterly loss after bad bets on risky mortgages.

After Citigroup with 2.7 percent, the institutions with the lowest delinquency rates were, in order of lower to higher, First Horizon National Corp (FHN.N), UBS AG (UBSN.VX), Bank of America Corp (BAC.N) and American Home Mortgage Investment Corp (AHMIQ.PK), S&P said. (Reporting by Al Yoon; Editing by Jonathan Oatis)