The Seattle metro index posted a 7.3 percent gain for the 12 months ended in July, outpacing the 5 percent gain of the 20-city Case-Shiller index.

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The average price of existing single-family homes in King, Snohomish and Pierce counties slipped 0.1 percent in July from the previous month, yet still was ahead of a 20-city index, according to Standard & Poor’s/Case-Shiller index data released Tuesday.

July’s performance was a reversal from June’s, when the Case-Shiller home-price index for the Seattle metro rose 0.1 percent over May, after taking seasonal fluctuations into account. Meanwhile, the 20-city index’s 0.2 percent decline in July repeated June’s performance.

Over the year, the Seattle metro index posted a 7.3 percent gain, outpacing the 20-city index’s 5 percent gain, according to S&P Dow Jones Indices, publisher of the index. July was the fourth consecutive month of slowing 12-month price gains.

Nationally, home prices rose at a solid pace in July, as would-be buyers competed for a diminished supply of available housing.

The Case-Shiller 20-city index’s 5 percent annual increase is up from a 4.9 percent annual pace in June.

San Francisco and Denver, where the price indexes gained more than 10 percent over the year, were the only metros with double-digit increases. Washington, D.C., had the weakest gain over the year — 1.7 percent — in average home prices.

Fourteen of the 20 metros saw annual price gains accelerate in July, with Phoenix marking its eighth consecutive month of year-over-year gains, the longest streak among the metros in July.

Steady job growth and an economic recovery in its seventh year have encouraged more Americans to buy homes. That lifted sales to an eight-year high in July. Yet those buyers have bid up prices in many areas because the number of homes for sale remains limited.

“Prices of existing homes and housing overall are seeing strong growth and contributing to recent solid growth for the economy,” said David Blitzer, chairman of the publisher’s index committee, in a statement. He pointed to investment in housing, furniture and household equipment all outpacing overall economic growth.

Nationally, the current housing inventory is equal to 5.2 months of sales, below the six months that is typical in a balanced housing market.

Seattle-based Zillow, which tracks home prices as well, said the median home price of single-family homes in King, Snohomish and Pierce counties in July was $371,100, up 6.9 percent over the year.

While Case-Shiller’s index is based on just those homes that sold over the last three months, Zillow’s index includes all homes in a market, using recent sales as one of several factors in estimating price trends.

“The market is continuing to heal and find its footing in a new environment, one where highly local factors — including local job opportunities, household formation and income growth — matter more in local markets than national trends,” said Zillow chief economist Svenja Gudell.

Consistent price gains can make homeowners feel wealthier and more likely to spend, providing a boost to the economy. Higher home values also reduce the number of Americans who owe more on their mortgages than their homes are worth, a condition known as being “under water.”

Still, housing faces several challenges in the coming months. Prices are rising at more than double the rate of wages, which have increased just 2.2 percent in the past 12 months. That is likely pricing many would-be buyers out of the market.

And while mortgage rates are still low, they could be headed up soon. Federal Reserve Chair Janet Yellen has indicated that the Fed may raise short-term rates for the first time in nine years before the end of the year. That would eventually push up mortgage rates.

Blitzer, of S&P Dow Jones Indices, isn’t worried.

“An interest-rate increase by the Federal Reserve, now expected in December by many analysts, is not likely to derail the strong housing performance,” he said.

Still, rising prices and expectation of higher mortgage rates may already be weighing on sales of existing homes. Sales slid nearly 5 percent in August from July’s eight-year high to the lowest level since April, the National Association of Realtors said last week.

And fewer Americans signed contracts to buy homes in August. That suggests sales may slip further in the coming months. A signed contract typically precedes a completed sale by one or two months. Still, existing home sales are 6.2 percent higher than a year ago.