The National Association of Realtors announced this morning that existing home sales fell off in February, sliding 9.6% to a seasonally adjusted annual rate of 4.88 million units in February.

The association reported that the number was particularly stark as it followed an upwardly revised 5.40 million units in January.

“Housing affordability conditions have been at record levels and the economy has been improving, but home sales are being constrained by the twin problems of unnecessarily tight credit, and a measurable level of contract cancellations from some appraisals not supporting prices negotiated between buyers and sellers,” said NAR Chief Economist Lawrence Yun. “This tug and pull is causing a gradual but uneven recovery. Existing-home sales remain 26.4% above the cyclical low last July,” he added.

The association reported that a parallel survey found that first-time buyers purchased 34% of homes in February, up from 29% in January. This was an increase, but first-time buyer purchases were up 42% in February 2010.

All-cash sales made up a record 33% of sales in February, up from 32% in January; they were 27% in February 2010. Investors accounted for 19% of sales activity in February, down from 23% in January; they were 19% in February 2010. The balance of sales were to repeat buyers, the association said.