Unemployment among District of Columbia residents climbed one percentage point in January to a level of 8.1 percent, the highest jobless rate in the city since mid-1979, the D.C. Department of Employment Services reported yesterday.

For the metropolitan area as a whole, including both the city and suburbs, unemployment rose only 0.2 percent between December and January, reaching a regional total of 4.5 percent.

The changes reflected across-the-board declines in employment in government, retail trade, construction, finance and other industries in the region. One apparent factor was the end of a congressional term in which a large number of lawmakers retired or lost elections, leaving many staff members without jobs when Congress reconvened early in January.

Larry M. Thurston, who compiled the figures for the report, said President Reagan's federal job freeze order was not reflected in the statistics since it was not issued until after he took office Jan. 20.

"At this point I am not too worried about January because one month does not make a trend," Thurston said. He also said year-end adjustments in statistics may have magnified the jobless figure somewhat.

In January, 3,723 persons filed initial applications for unemployment compensation, a rise of 56 percent over the 2,387 claims in December.

The last time the D.C. jobless rate reached 8.1 percent was June 1979. In January, the D.C. rate narrowly exceeded the national unemployment rate of 7.4 percent.

In January 1980, the city's unemployment rate was 6.9 percent, with a total of 310,900 persons in the work force and 289,300 actually employed, leaving 21,600 jobless. The January 1981 figures, with their 8.1 percent rate, showed 306,900 in the work force and 281,000 employed, leaving 25,900 jobless.

While the unemployment rate -- the proportion of job-seeking workers without employment -- was greater in the city, in absolute numbers there were more suburbanites out of work -- 48,500. In January, the total metropolitan area joblessness was 73,400, with 1,617,300 District and suburban residents in the work force, 1,543,900 of them employed.

The biggest single decline in jobs between December and January was in federal, local and state government employment, which fell from 276,700 to 273,400.