Early this election season, Alexandria Democrat James P. Moran Jr. said he wanted to give 8th District Rep. Stan Parris a punch in the nose, and yesterday he did just that -- unseating the Republican incumbent in one of the most startling upsets the Northern Virginia suburbs have seen in years.

With 100 percent of precincts reporting, the Alexandria mayor had won 52 percent of the vote, compared with 45 percent for Parris.

Those numbers, stronger for Moran than even most of his ardent supporters had predicted, brought whoops and cheers of jubilation last night at the victory party at Alexandria's Radisson hotel, the theme song from "Rocky" blaring as the candidate came to the stage.

"This is a very strong victory," said Moran, 46, holding his 18-month-old son, Patrick. "The voters of Northern Virginia have sent a message loud and clear -- it's time for a change."

A few miles away, at the Springfield Hilton, Parris partisans were stunned and mostly silent, some of them in tears, as Parris's 25-year political career apparently reached a close. "I have no regrets," Parris said. "We did the very best we could under the circumstances."

Although Moran's congressional challenge came to be one of the nation's best-financed, it began almost as an accident. As late as last November, he was wavering about whether to make the run now or wait until after redistricting in 1992, which is expected to give Northern Virginia a new House district.

Moran was forced into the race when it became clear that another Democrat -- Mark Warner, a wealthy young campaign aide to Gov. L. Douglas Wilder -- could gain the inside track if Warner ran and defeated Parris.

Putting an end to a campaign that was memorable for its raucous and angry tone, Moran struck a lofty note last night. He quoted Hubert H. Humphrey, and promised to fight for children and the homeless, and against racial injustice.

His litany of causes, Moran said, "is not the definition of liberalism, it is the essence of humanity."

Yesterday's results were a study in how dramatically political fortunes can change.

For nearly a decade, Parris, 61, was considered unbeatable in his district, as he trounced Democratic challengers in 1984, 1986 and 1988. From this solid base he became one of the Washington area's most visible politicians, drawing attention particularly for his sharp-tongued attacks on the District of Columbia government and its management of the Lorton prison in his district.

Moran's career, by contrast, was seen as virtually dead just six years ago, when he resigned from the Alexandria City Council after his conviction on a misdemeanor conflict-of-interest charge. But Moran, a former congressional aide who was an accomplished boxer in his youth, came back as the mayor in 1985.

When he announced for Congress this year, many Democrats wished him luck but privately confided that he didn't have much chance.

But Moran's prowess as a fund-raiser allowed him to do something few challengers do: match the incumbent's spending. According to officials with both campaigns, the candidates raised about $900,000 each.

This financial parity allowed Moran to match Parris blow for blow in an expensive and vitriolic war waged with television commercials.

Because "Moran was able to keep on a par in fund-raising, he was able to get his message out to the people," said Mark J. Rozell, a Mary Washington College political scientist. "That's something many challengers can't do."