NEW YORK (CNNMoney.com) -- Mortgage rates climbed slightly higher this week, reaching their highest level in more than four years, Freddie Mac reported Thursday.

The average rate on the 30-year fixed-rate mortgage was 6.79 percent for the week ending July 6, up from 6.78 percent the week before. That's the highest level since late May 2002 when the 30-year loan rate stood at 6.81 percent.

A year ago, the 30-year mortgage rate averaged 5.62 percent.

"Since last week's rate increase by the Federal Reserve came as no great surprise, mortgage rates remained nearly unchanged from the previous week," Frank Nothaft, Freddie Mac vice president and chief economist. said in a statement.

"This is fairly consistent with our economic outlook, which continues to forecast that the interest rate for the 30-year fixed-rate mortgage will gradually drift upward, but should remain under seven percent for the year," said Nothaft.

Further rate hikes by the Fed could help push mortgage rates higher still, though home loan rates are more closely tied to the Treasury market than to the Fed's short-term rate target.

Freddie Mac also said the average rate on 15-year fixed-rate mortgages rose to 6.44 percent from 6.43 percent the previous week. A year ago, that loan averaged 5.20 percent.

The last time the 15-year fixed-rate mortgage reached this level was in April 2002.

Five-year adjustable-rate mortgages remained unchanged from last week, averaging 6.39 percent. The five-year ARM averaged 5.19 percent a year ago.

The average one-year adjustable-rate mortgage (ARM) edged higher to 5.83 percent from 5.82 percent. At this time last year, the one-year loan averaged 4.33 percent.

For homeowners using adjustable rate mortgages, a rise in interest rates can mean ballooning payments.

The Mortgage Bankers Association estimates that some $330 billion worth of ARMs will adjust in 2006 and $1 trillion worth will reset by the end of 2007. With a $200,000 loan adjusting upward from 4 percent to 6 percent, the monthly bill would increase to about $1,200, from $955.

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