WASHINGTON — Mortgage rates around the country rose for a second straight week but still remain below rates seen a year ago.

In its weekly survey, mortgage giant Freddie Mac reported yesterday that rates on 30-year, fixed-rate mortgages increased to 5.66 percent, up from last week's 5.62 percent. The increases were coming after rates had dipped to 5.53 percent in the last week of June, the lowest point for 30-year mortgages in 14 months.

Except for two weeks in late March, 30-year mortgages have been below 6 percent all year. The low rates have powered a boom in sales of both new and existing homes.

There are worries that a housing bubble could be forming in hot sales areas with strong demand pushing home prices to levels that will not be sustainable.

Analysts attributed the rate increases of the past two weeks to financial markets moving to a view that the economy will expand at a stronger pace this year than previously believed.

But analysts continue to forecast that mortgage rates will rise at a gradual pace, matching moderate, quarter-point increases in short-term rates expected from the Federal Reserve.

"Over the past few weeks, financial markets have been gearing up for greater growth in the economy, which ultimately leads to higher inflation rates," said Frank Nothaft, Freddie Mac's chief economist.

Nothaft said since 2000, the 30-year mortgage has averaged 6.6 percent, nearly a full percentage point above the current level.

Rates on 15-year, fixed-rate mortgages, a popular choice for refinancing a home mortgage, averaged 5.25 percent this week, up from 5.20 percent last week.

For one-year adjustable rate mortgages, rates rose to 4.39 percent this week, compared with 4.33 percent last week. Rates on five-year hybrid adjustable rate mortgages averaged 5.15 percent this week, down slightly from 5.19 percent last week.