WASHINGTON — Fewer Americans bought homes in August, as investors retreated from real estate and first-time buyers remained scarce.

Sales of existing homes fell 1.8 percent to a seasonally adjusted annual rate of 5.05 million, the National Association of Realtors said Monday. That snaps a four-month streak of gains. August sales are down from a July rate of 5.14 million, a figure that was revised slightly downward.

Much of the decline came from the exodus of investors, who had been buying properties in the aftermath of the housing bust and recession. Investors accounted for just 12 percent of August purchases, compared to 17 percent a year earlier.

Overall, the pace of home sales has dropped 5.3 percent year-over-year.

The rebound from the housing bust that triggered the recession has been painfully slow. The share of Americans who own homes has trended downward over the course of the five year recovery, as more Americans are becoming renters. The ownership rate fell to 64.7 percent through the middle of this year, down from a peak of 69.2 percent toward the end of 2004, according to the Census Bureau.

Sales were curbed by winter storms earlier in the year. They began to accelerate through the summer as mortgage rates eased back from 52-week highs. But the combination of rising home prices last year and sluggish wage growth has limited sales.

Rising prices through much of 2013 and weak income growth priced out many would-be buyers. Only 29 percent of purchases in August came from first-time buyers, well below the historical average of 40 percent.

The median sales price has risen 4.8 percent over the past 12 months to $219,800, but it slipped slightly in August compared to prices in July and June.

Sales of existing homes continue to lag last year’s pace of 5.1 million. Annual sales of 5.5 million are consistent with a healthy housing market, according to analysts.