U.S. home prices continued to rise in the second quarter but showed the biggest slowdown in three decades, federal regulators reported Tuesday.

The figures released by the Office of Federal Housing Enterprise Oversight, the agency that oversees the big mortgage-finance companies Fannie Mae (FNM) and Freddie Mac (FRE), provided the latest indication that the housing market is cooling substantially.

Average home prices rose 1.17 percent in the April-June period, compared with 3.65 percent in the second quarter of 2005 -- the biggest decline in price growth since OFHEO started keeping track of home prices in 1975, the new report showed.

The agency cited higher interest rates and rising inventories of homes for sale as possible factors in the slowdown in price growth.

"These data are a strong indication that the housing market is cooling in a very significant way," OFHEO Director James B. Lockhart said in a statement. "Indeed, the deceleration appears in almost every region of the country."

Data issued last month provided proof that the housing boom is over. The Commerce Department reported that sales of new homes dropped in July by 4.3 percent, the largest amount since February, while the inventory of unsold homes climbed to a record high. And sales of previously owned homes fell 4.1 percent in July to a 2 1/2-year low, according to the National Association of Realtors.

Sales of both new and existing homes set records for five consecutive years as the housing industry enjoyed a boom powered by the lowest mortgage rates in four decades. But rates have been steadily rising this year as the Federal Reserve tightens credit conditions as a way to slow the economy and keep inflation under control.

Analysts expect home sales to drop by some 10 percent this year.

Still, the OFHEO report noted, house prices grew faster from the second quarter of 2005 to the same period this year -- by 10.06 percent -- than did prices of other goods and services, which rose 4.41 percent.

The second-quarter figure is derived from an average of home prices in April, May and June. Prices in that April-June period were up 1.17 percent from the first quarter of the year -- the smallest rate of quarterly price growth since a 1.12 percent gain in the fourth quarter of 1999, OFHEO said.