WASHINGTON — Average U.S. rates on fixed mortgages rose slightly this week, staying near three-month lows. Rates could fall next week now that lawmakers reached a deal to avert a possible government debt default and reopen the federal government.

Mortgage buyer Freddie Mac said Thursday that the average rate on the 30-year loan increased to 4.28 percent from 4.23 percent last week. The average on the 15-year fixed loan edged up to 3.33 percent from 3.31 percent.

Rates are likely to fall even lower now that Congress reached a deal to reopen the government and allow the Treasury to borrow normally until early February.