U.S. applications for mortgages to buy a home slipped to their weakest level in about 4½ months last week as home borrowing costs held steady or were higher, the Mortgage Bankers Association said.

The Washington-based group's seasonally adjusted barometer on purchase mortgage activity, a proxy on future home sales, fell 2.0 percent to 235.4 in the week ended July 28. This was the lowest reading since 235.3 in the March 17 week.

Analysts have blamed the downturn in home sales largely on a shortage of properties available for sale rather than a softening in housing demand with financing costs hovering near historic low levels.

Interest rates on conforming 30-year fixed-rate mortgages averaged 4.17 percent for a second week.

Conforming loans are those with balances of $424,100 or less that qualify for guarantees from federal mortgage agencies Fannie Mae and Freddie Mac.

Average rates on other types of mortgages that the MBA tracks were unchanged to 5 basis points higher than in the prior week.

The MBA's seasonally adjusted gauge of refinancing applications fell 3.8 percent to 1,361.0.

The group's barometer on total mortgage applications adjusted for seasonal factors declined by 2.8 percent to 406.6.