WASHINGTON, April 24 (Reuters) - Average interest rates on U.S. 30-year mortgages fell for a second straight week in the week ending April 25, Freddie Mac said on Thursday, as continued economic weakness kept mortgage rates low.

Thirty-year mortgage rates dipped to an average of 5.79 percent from 5.82 percent last week.

Fifteen-year mortgages and one-year adjustable rate (ARM) mortgages were unchanged in the week. Fifteen-year mortgages remained at an average of 5.12 percent and the ARM at 3.79 percent.

"A tepid national economy has anchored mortgage rates to current low levels so far this year," Frank Nothaft, Freddie Mac's chief economist, said in a statement.

"However, according to the Federal Reserve's Beige Book, the housing industry is the only bright spot in the economy right now. That is due primarily to low mortgage rates," Nothaft said.

The Fed on Wednesday said the Iraq war kept U.S. consumers wary in March and early April, leaving overall economic activity "lackluster."

"Most districts continued to report weakness in manufacturing, although some pockets of growth were noted in most of the reports. Businesses continued to report a cautious attitude toward spending, and commercial real estate was reported to still be in a slump," the Beige Book stated.

On Friday the Commerce Department will issue U.S. Gross Domestic Product for the first quarter of 2003. "That should give us a more definitive look at shape of the economy," Nothaft said.

Two housing reports will also be issued later on Friday. Commerce will release U.S. March single-family home sales and the National Association of Realtors will issue U.S. existing home sales for that month.