NEW YORK (CNN/Money) - Long-term mortgage rates fell slightly this week after rising last week, according to a survey released Thursday, but refinancing levels declined despite low rates as many people have already re-mortgaged, economists said.

Freddie Mac reported that the 30-year mortgage averaged 6.81 percent in the week ending May 24, with an average of 0.7 point payable up front to the lender. The rate moved slightly lower from last week's average of 6.89 percent. The 30-year mortgage averaged 7.20 percent a year ago.

The 15-year fixed-rate mortgage averaged 6.28 percent, down from 6.37 percent last week and down from 6.74 percent a year ago. The 15-year averaged 0.7 point payable up front.

In addition, one-year adjustable-rate mortgages rose to 4.85 percent, with an average 0.7 of a point due up front, up slightly from 4.81 percent last week and down from an average of 5.85 percent a year ago.

"Although mortgage rates are at generationally low levels, refinancing should start to drop off, as just about everyone who had an incentive to refinance into a lower rate has done so," Freddie Mac chief economist Frank Nothaft said. "In the present economic environment, most who are refinancing now are doing so to take out some of the equity that has been building up over the last few years."

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Freddie Mac (FRE: down $1.01 to $64.91, Research, Estimates), or Federal Home Mortgage Corp., is a publicly traded company the government established in 1970 to provide a flow of funds to mortgage lenders. It buys mortgages from banks, bundles them and then resells them as mortgage-backed securities. Its products, and the products of other similar entities, have become increasingly popular as an alternative to government-backed bonds, particularly with international investors.