NEW YORK, May 15 (Reuters) - Five U.S. Federal Home Loan Banks delayed filing first-quarter reports with the Securities and Exchange Commission on Friday as they move to adopt a uniform way of reporting losses on some of their mortgage bond holdings.

As a result, the combined quarterly report from the FHLB system will also be delayed.

Federal Home Loan Banks are 12 regional institutions that are chartered by the U.S. Congress to raise money for member banks' mortgage and small business lending.

All 12 banks are moving to adopt a common framework for determining certain losses related to hard-to-price bonds made up of pools of home loans, under recent guidance provided by their regulator, the Federal Housing Finance Agency.

The banks of Boston, Chicago, Pittsburgh, Seattle and Topeka have told the SEC their first quarter 10-Qs will be delayed.

Poor underwriting during the housing boom of recent years, followed by falling house prices in the past two years created a huge number of defaulted mortgages. Some of those mortgages were bought by FHLBanks and have led to losses, hurting their balance sheets.

In April 2008 the Federal Home Loan Bank of Chicago halted its program of purchasing mortgage loans, citing onerous costs.

The bank in the past decade had been criticized for lax interest-rate risk management, in part due to the growth of the program known as the Mortgage Partnership Finance, or MPF, analysts said. The bank launched the program in the late 1990s to share the risk of managing mortgages with lenders.

The seven other banks have field 10-Qs with the SEC.