Colonial BancGroup controls 25% of all warehouse-lending funds. If that money disappears, mortgage loans will be even harder to get.

Aug. 27 (Bloomberg) -- Mortgage rates for 30-year fixed home loans rose this week even as the year’s record low borrowing costs produced the biggest jump in new home purchases in four years.

The average 30-year rate increased to 5.14 percent from 5.12 percent, mortgage buyer Freddie Mac of McLean, Virginia, said today in a statement. The 15-year rate was 4.58 percent.

“Rates are fairly stable and low right now,” said Celia Chen, senior director at Moody’s Economy.com in West Chester, Pennsylvania. “Conditions are looking more positive than they have for a long time.”

Climbing mortgage rates may threaten a gain in home sales spurred by falling home prices, a government tax credit for first-time buyers, and a Federal Reserve program designed to lower borrowing costs. New home sales jumped more than forecast in July and sales of existing homes rose to the highest in almost two years.

The Federal Reserve set out last year to lower mortgage rates by buying bonds backed by home loans. It increased the size of its program to $1.25 trillion in March. Those bond purchases from Fannie Mae, Freddie Mac and Ginnie Mae brought down yields on mortgage-backed securities and allowed lenders to reduce rates on new loans while still selling the securities backed by them at a profit.

The plan helped cut mortgage rates to a record low 4.78 percent twice in April.

Sales Increase

Rates started climbing in May along with Treasury yields on investor concern that higher government debt would fuel inflation. The 30-year mortgage rate climbed to 5.59 percent in the week ended June 11 and has since fallen back.

New-home sales increased 9.6 percent in July, the most since February 2005, to a 433,000 annual pace, the Commerce Department said yesterday. The number of houses on the market dropped to the lowest level in 16 years.

Existing home sales advanced 7.2 percent in July, putting the market on pace for 5.24 million sales this year, the most since August 2007, the National Association of Realtors said last week. The gain was the biggest since records began in 1999.

The Mortgage Bankers Association’s index of applications to purchase a home or refinance a loan increased 7.5 percent to 566.4 in the week ended Aug. 21 from 527 in the prior week. The group’s refinancing gauge jumped 13 percent, while the index of purchases advanced 1 percent.