WASHINGTON — Rates on 30-year mortgages dropped below 6 percent this week for the first time in more than a month, reflecting aggressive efforts by the Federal Reserve to cut interest rates to protect the economy from a serious recession.

Freddie Mac, the mortgage company, reported yesterday that 30-year fixed-rate mortgages averaged 5.87 percent this week. That was down from 6.13 percent last week and marked the first time that 30-year rates have fallen below the 6 percent level since the week of Feb. 14.

Rates on 30-year mortgages dropped below the 6 percent threshold in the second week of January and stayed there for six straight weeks as the sharp economic slowdown stirred concerns about a possible recession.

Other categories of mortgages also showed declines this week.

Rates on 15-year fixed-rate mortgages, a popular choice for refinancing, fell to 5.27 percent this week, down from 5.60 percent last week.

For five-year adjustable-rate mortgages, rates dipped to 5.56 percent, compared with 5.58 percent last week.

Rates on one-year adjustable-rate mortgages were the only category to increase, edging up to 5.15 percent, compared with 5.14 percent last week.