Would-be homebuyers, such as James Aberle, have watched with angst as mortgage rates have jumped nearly 10 percent in just five weeks. The average rate on a 30-year fixed mortgage hit 6.74 percent this week, Freddie Mac said yesterday, its highest point in nearly a year.

The spike in rates — which averaged just 6.15 percent in mid-May — could have a whiplash effect on the market if they stay high. In the short term, it could force fence-sitting buyers to make an offer. Mortgage applications for purchases, for instance, rose 7 percent last week. But over the long term, higher rates are likely to depress home sales and prices by making mortgages too expensive for some.

That's especially true in such states as California, Arizona and Florida, where prices are out of reach for many working families.

"My fingers are hurting from keeping them crossed, hoping the mortgage rates go back down," says Aberle, 39, a marketing manager.

Last weekend, he found a home in Phoenix he wants to buy, but he isn't allowed to lock in a mortgage rate until next week.

"Interest rates have gone up more strongly and more quickly than we had anticipated," said Frank Nothaft, Freddie Mac's chief economist. Where they go from here "depends on upcoming economic news, but I see interest rates moving within a range of no less than 6 1/2 and as high as 6 7/8."

Nothaft largely blames rising international interest rates, which have put pressure on U.S. rates to go higher to attract investors.

Zooming interest rates also make it more expensive for those with adjustable-rate mortgages to refinance into fixed-rate loans.

The 15-year fixed rate rose to 6.43 percent from 6.22 percent last week, Freddie Mac reported. Five-year adjustable and one-year adjustable rates rose also. The five-year rate went up from 6.24 percent to 6.37, and the one-year ARM rose from 5.65 percent to 5.75 percent.