Walter F. Mondale didn't spend a day campaigning in his adopted home of the District of Columbia, and when it came time to call it quits and await the voters' verdict, he headed back to his home state of Minnesota.

But it was here in the District -- a tiny oasis of more traditional Democratic liberalism and black political activism -- that Mondale scored one of his few electoral victories against President Reagan, who last night won an impressive election sweep.

Bill Kennard, a young black lawyer who lives in Northwest Washington and voted for Mondale, pondered yesterday the prospects of living in a city-state that seems so totally out of step with the rest of the nation.

"I would hope D.C. is reflective of the nation," Kennard said outside the polls at Lafayette School. "But the more I read, the more I think D.C. is a little microcosm apart."

Carman Dickerson, who recently lost her job as a payroll technician, said one has to be philosophical about the relative powerlessness that comes with living in a city with a population of over 638,000 with only three electoral votes and no vote in Congress.

"I feel you just have to get out there and try and try again, and do what you believe in and hope for the best," Dickerson said after voting at the Fort Stevens Recreation Center, near 13th & Van Buren streets NW.

But one staunch D.C. Democrat, who works for a political action group, turned to his wife as she was leaving the house to vote and said: "Why bother? Your vote doesn't matter in the District anyway."

The District of Columbia, where 80 percent of the 274,810 registered voters are Democrats, has been hostile territory for Republicans since 1964, when the city was granted home rule. That year, the city contributed to President Johnson's landslide reelection victory, and has been voting for Democratic presidential nominees ever since.

In 1980, President Carter defeated challenger Ronald Reagan in the District with 75 percent of the vote. It was one of the few scraps of good news for Carter in his devastating loss to Reagan.

Mondale clearly was not the favorite of D.C. Democrats at the start of the 1984 political season -- Jesse L. Jackson, the first black to mount a serious campaign for the White House, took the 70 percent black District by storm in the May 1 presidential primary. But local leaders, including Mayor Marion Barry, lined up behind Mondale, and a victory here for the Democratic nominee was never in doubt.

Yesterday, D.C. voters trekked to voting booths in record numbers and delivered about 85 percent of their vote for Mondale, despite polls that projected a landslide Reagan victory. Many said it was important to make a statement.

"Mondale is not going to win, but I voted for him," said Bernice Tillett, a resident of Ward 4, a largely black, middle-class area of Northwest. "Reagan is antipoor, antiblack and antielderly. He may be a nice man."

An economic consultant from Georgetown said he voted for Reagan in 1980, but this time is supporting Mondale. "I voted against my pocketbook because I think Mondale is less likely to take us into bombings and Central America," he said.

Of course, not everyone shares those views. Reagan has won some converts among blacks, who have found virtue in the president's conservative economic and tax policies. D.C. Del. Walter E. Fauntroy scoffs at the notion that Reagan has much black support, however, judging that it is limited to perhaps "those who are making $200,000 a year or more."