WASHINGTON - U.S. mortgage rates have suddenly jumped from near-record lows and are adding thousands of dollars to the cost of buying a home.

The average rate on the 30-year fixed loan soared this week to 4.46 percent, according to a report Thursday from mortgage buyer Freddie Mac. That's the highest average in two years and a full point more than a month ago.

The surge in mortgage rates follows the Federal Reserve's signal that it could slow its bond purchases later this year. A pullback by the Fed would likely send long-term interest rates even higher.

In the short run, the spike in mortgage rates might be causing more people to consider buying a home soon. Rates are still low by historical standards, and would-be buyers would want to lock them in before they rise further.

But eventually, more expensive home loans could price some people out and slow the housing market's momentum, which has helped drive the U.S. economy over the past year.

"People are getting off the fence a little bit more or choosing to buy now instead of choosing to buy three months from now," said Anthony Geraci, a Cleveland real estate broker-owner who says he's seeing more sales activity lately in his market.

Mortgage rates are rising because they tend to track the yield on the 10-year Treasury note, a benchmark for most long-term interest rates. The 10-year yield began rising from near-record lows in May after speculation grew that the Fed might be closer to reducing its bond purchases.

In early May, the average rate on a 30-year mortgage was 3.35 percent, just above the record low of 3.31 percent.

But rates began to surge - and stocks plunged - after Fed Chairman Ben Bernanke made more explicit comments last week about the Fed's plans. He said the Fed would likely scale back its bond buying later this year and end it next year if the economy continued to strengthen.

The rate on 30-year loan soared from 3.93 percent last week to 4.46 percent this week - the biggest one-week jump in 26 years.

The effect on buyers' wallets in just the past two months is striking.

A buyer who locked in a 3.35 percent rate in early May on a $200,000 mortgage would pay $881 a month, according to Bankrate.com. The same mortgage at a 4.46 percent rate would run $1,008 a month.

The difference: $127 more a month, or $45,720 over the lifetime of the loan. Those figures don't include taxes, insurance or initial down payments.

Jed Kolko, chief economist at Trulia, a real estate data analysis firm, thinks many would-be buyers will start to take note.

"Some buyers will reconsider jumping into the market; others will speed up their (home) purchases before rates go higher," Kolko said.

The rate hike comes at a critical time. Low mortgage rates have helped fuel a housing recovery that has kept the economy growing modestly despite higher taxes and steep federal spending cuts.

In May, completed sales of previously occupied homes surpassed the 5 million mark for the first time in 3? years. And those sales could rise further in June because the number of people who signed contracts to buy homes rose last month to the highest level since December 2006. There's generally a one- to two-month lag between a signed contract and a completed sale.

Greater demand, along with a tight supply of homes for sale, has driven up home prices. It's also led to more home construction, which has created more jobs and contributed to economic growth.

Lower rates have also inspired a refinancing boom over the past two years. Many homeowners have locked in rates below 4 percent. That has lowered their monthly payments, leaving them with more cash to spend elsewhere and fuel more economic growth.

The average rate on a 15-year fixed mortgage, a popular refinancing instrument, soared this week to 3.50 percent - its highest point since August 2011 - from 3.04 percent last week.

A report this week suggested that the economy might not be as strong as some had thought. The government cut its growth estimate for the January-March quarter to an annual rate of just 1.8 percent - much lower than the 2.4 percent rate it estimated a month ago.

A key reason for the downgrade was that consumers spent less than previously thought. Less spending has led some economists to predict that growth will stay weak through the summer and fall short of the Fed's more optimistic forecast of 2.3 percent to 2.6 percent growth for all of 2013.

The downgrade for economic growth has cast some doubt on the likelihood that the Fed will reduce its stimulus later this year. Several Fed voting members have stressed in recent days that Bernanke's comments made clear that any pullback in bond purchases would hinge on the economy's performance, not a calendar date.

Those reassurances and solid, if not spectacular, economic data have helped boost stocks in recent days and reverse a jump in long-term interest rates. The yield on the 10-year Treasury note fell Thursday to 2.47 percent, down from its two-year high of 2.66 percent on Monday.

Geraci says he doesn't think higher mortgage rates will hurt a housing market in which there aren't nearly enough available homes in many areas.

"So buyers that find a nice home, no matter what the rates are, are going to move on it," Geraci said. "If there's enough supply, people might sit and wait a little bit and see if the rates come down."

Rising rates motivated Alex Backus to act two weeks ago and sign a contract on a $365,000 three-bedroom house in the Seattle suburb of Edmonds, Wash.

Backus, 30, had searched listings for two months before signing the contract. He locked in a 30-year loan at a fixed rate of 4.125 percent.

"Seeing that interest rates were starting to come back up, it seemed like now was the time to really start to get serious about buying a home," said Backus, an aerospace engineer.