Housing became slightly less affordable in the first quarter because of rising interest rates, according to the National Association of Realtors.

The group said its housing affordability index fell 1.4 points in the first quarter to 125.5. It also revised its index downward to 126.9 in the preceding quarter, from 136.1.

"Rising rates definitely robbed buyers of some purchasing power," said Edmund G. Woods, the group's president. "The impact is far more noticeable among first-time buyers than those trading up."

The average mortgage interest rate in the first quarter was 8.12%, the NAR said, up from 7.82% in the fourth quarter and up from 6.91% in the first quarter of 1994.

The affordability index, which measures the ability of a typical American family to buy a home, means that a family earning the median annual income of $38,528 in the first quarter had 125.5% of the income needed to qualify for a conventional mortgage covering 80% of the median price of an existing home.

The median home price last quarter was $107,700, down from $108,400 in the preceding quarter, according to the association.

Despite the latest decline, housing remains highly affordable. In 1989, the index averaged just 108 and climbed steadily to a peak of 136.7 in the first quarter of 1994, when the Fed started pushing interest rates upward.

The NAR also compiles an affordability index for first-time buyers, and this tells a very different story. In the first quarter, the index stood at 81.5%. This meant that the typical first-time buyers were only able to afford a home substantially cheaper than the median price of a starter home, assuming a down payment of 10%.

Special programs that permit down payments smaller than 10% would make higher-priced starter homes accessible to the typical first-time buyer.

"Rising rates are a continuing disadvantage facing first-time homebuyers as the differential between affordability for move-up and entry-level buyers becomes more evident," said John A. Tuccillo, NAR's chief economist. "This trend has been apparent in the recent drop in sales of existing single-family homes."

Mr. Woods used the announcement to underscore his group's opposition to any attack on the mortgage interest deduction. "If the deduction is reduced, many families would be unable to afford a home in their current housing market," he said. "The after-tax cost of buying a home would rise dramatically."

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