NEW YORK - Homeowners who delayed locking in super-low mortgage rates - think close to 4 percent for a 30-year fixed - may have waited too long.

Rates are creeping back up. Now those in the market to buy or refinance have to decide whether to take what's available or risk making the same mistake twice.

Freddie Mac, the government-backed company that buys and sells mortgages, said yesterday that average rates on 15- and 30-year fixed loans increased sharply from last week. It was the fourth straight weekly rise. Fixed rates had been the lowest in decades.

"People thought for a while that rates would fall below 4 percent, and they hedged on that," said New York mortgage broker and banker Andrew Toolin, who had just been on the phone with a client who is paying 5.875 percent on his mortgage.

A month ago, the client passed on what now looks like a once-in-a-lifetime opportunity: the chance to refinance at 4.125 percent. That would have put $321 more in his pocket each month.

He held out, thinking he could do even better. Now the rate is up to 4.75 percent. He could still shave money off his monthly mortgage payment, but not nearly as much - about $229.

"He's wondering if he should wait for rates to go back down," Toolin said. "He's talking to his wife tonight about what to do."

Rates are rising because they tend to follow the trends set by government bonds, like the 10-year Treasury bond. Investors are selling those bonds, causing their interest rates to rise.

Even though they're rising, mortgage rates remain at extraordinarily low levels by historical standards. The average rate on the 30-year mortgage rose to 4.61 percent from 4.46 percent last week. It hit 4.17 percent a month ago, the lowest level in the 40 years that comparable records have been kept.

The rate on a 15-year fixed loan, a popular refinancing option, rose to 3.96 percent. Rates hit 3.57 percent last month, the lowest since 1991.