Even as the rest of America pulls back on mortgages, the wealthy are going on a borrowing binge.
New data from RealtyTrac show that wealthy buyers are ramping up their use of mortgages to buy homes. In July, 46 percent of people buying houses ranging from $2 million to $5 million used mortgages—up dramatically from 27 percent a year earlier. With purchases of $1 million to $2 million, the use of mortgages jumped to 63 percent from 49 percent.
The mortgage spree stands in stark contrast to the rest of the country, which has seen mortgage activity decline with rising rates. Nationwide, 40 percent of houses sold in July were bought with cash, up from 31 percent in July 2012, according to RealtyTrac.
(Read more: Want a house? Seewhat $1 million gets you)
Housing economists and luxury real estate brokers say the mortgage economics for the wealthy are different than for everyone else. While rising rates make borrowing and buying less affordable for everyday homebuyers, looming rate hikes act as an incentive for affluent borrowers, who use loans as financial tools.
As rates start to rise, housing experts say, the wealthy who were waiting on the sidelines to buy or borrow decide to jump in. They are scooping up the cheap capital before it gets more expensive.
"With mortgage rates picking up, some of these folks decided to get off the fence and take advantage of the low rates," said Daren Blomquist of RealtyTrac. "With the wealthy it's more of a financial decision."
The borrowing spree by the wealthy reflects a growing divide in the mortgage market. Interest rates on jumbo mortgages—loans over $417,000 in most areas and over $625,500 in higher-priced areas—are now lower than rates for so-called conforming loans below those levels. It's highly unusual for jumbo loans to be cheaper than conforming loans, as the latter are traditionally backed by government agencies. Banks are cutting their mortgage staffs amid a big fall in applications and refinancing.
(Read more: Fannie, Freddie making billions—why shut them down?)
But uncertainty over the government's role in the mortgage market has added to the upward pressure on conforming rates. What's more, many banks see wealthy borrowers as more attractive borrowers. And many banks use mortgages to wealthy clients as a way to win their wealth-management and investment business.
(Read more: For sale: Mansion, Bentley, toilet brushes included)
Of course, cash remains king at the very top of the real estate market. More than three-quarters of buyers of homes priced at $5 million or more used cash for their purchases in July—up from 56 percent last year.
Olivia Hsu Decker, a top luxury real estate broker in San Francisco, said the superwealthy today have plenty of excess cash, and some don't like to bother with the complicated and time-consuming mortgage process. Buyers often can get a better sale price if they pay in quick cash rather than waiting on a loan.
"Mortgages are not easy, even for the wealthy," she said. "They'd rather just write a check."
Decker added, however, that many rich people get mortgages after they purchase, to take advantage of the cheap money.
(Read more: Yep, it's another housing bubble )
Other brokers add that the surge in mortgage rates and activity among wealthier buyers has driven a corresponding jump in sales—especially for second homes. Sales in the Hamptons were the highest ever in the second quarter, totaling $1.15 billion. Sales in Palm Beach, Fla., Aspen, Colo., and other high-end locations have also remained strong.
But some housing economists wonder if the high-end borrowing binge is temporary.
"The first half of the year was about pent-up demand and rising rates," said Jonathan Miller of the appraisal firm Miller Samuel. "A lot of that has played out, so I think you could see some decline in mortgages. But that will be determined by how fast rates rise."
—By CNBC's Robert Frank. Follow him on Twitter @robtfrank.