WASHINGTON — Rates on 30-year mortgages increased this week for the fourth time in the past five weeks.

Freddie Mac, the mortgage company, reported yesterday that 30-year fixed-rate mortgages averaged 6.13 percent this week, up from 6.03 percent last week.

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 economic slowdown stirred concerns about a possible recession.

All categories of mortgages showed increases this week.

Rates on 15-year fixed-rate mortgages, a popular choice for refinancing, rose to 5.60 percent this week, up from 5.47 percent last week.

For five-year adjustable-rate mortgages, rates rose to 5.58 percent, compared with 5.34 percent last week. And, rates on one-year adjustable-rate mortgages averaged 5.14 percent this week, up from 4.94 percent last week.