Ronald Reagan swept to a decisive victory in Virginia yesterday, taking virtually every section of the state in a landslide that ousted Reps. Joseph L. Fisher and Herbert E. Harris II, Northern Virginia's two liberal Democratic congressmen.

Reagan was expected to carry the conservative southern state but the dimension of his victory surprised even most ardent supporters. With all but one percent of the vote counted, the Republican nominee had a commanding 53-to-40-percent lead over President Carter with 5 percent for independent John Anderson in the contest for Virginia's 12 electoral votes.

Carter dragged down fellow Democrats Fisher of Arlington and Harris of Fairfax County, both three-term House members elected to Congress in the 1974 "Watergate" elections.

Both incumbents had made strong efforts to run independently of Carter, but both were apparently unable to shake off charges that they were loyal to the president. Harris also was plagued by a third candidate, a woman who ran on a pro-marijuana ticket and may have pulled enough votes from the incumbent to cost him the election.

"It [the defeat of Harris and Fisher] was definitely because of cocktails," said Virginia political scientist Larry Sabato, who said the Reagan triumph gave both Wolf and Parris between three and five extra points -- enough to ensure their victories.

"This was not a referendum on Joe Fisher," Lt. Gov. Charles S. Robb of McLean, next year's likely Democratic gubernatorial candidate, told the defeated congressman's supporters last night. "It is a very serious indictment of the economy."

Fisher's GOP opponent, Vienna lawyer-lobbyist Frank Wolf, pulled 52 percent, or 105,554 votes, to Fisher's 48 percent, or 98,648, with only a few absentee ballots uncounted.

Harris lost to GOP challenger Stanford Parris, the man he defeated to take the seat in 1974, by a slim margin of about 2,100 votes. His final margin was 51 percent to 49 percent, or 91,946 to 89,816. Harris refused to concede last night and Parris predicted his opponent would demand a recount.

Reagan's overwhelming victory over the president in Northern Virginia, once considered one of the state's most liberal and Democratic areas, far eclipsed Gerald Ford's win over Carter four years ago. Final totals showed Reagan led Carter by a stunning 56 percent to 33 percent margin in the Washington suburbs, with Anderson drawing 10 percent. Reagan's vote totaled 229,466 to 135,018 for Carter and 40,470 for Anderson. r

Statewide, Reagan took nine of Virginia's 10 congressional districts, with Carter squeezing out only a narrow victory in the usually overwhelmingly Democratic 4th District in Southeastern Virginia.

The only area Democrat to survive the GOP sweep was Arlington County Board candidate John G. Milliken, who hung onto a seat being vacated by another Democrat.

The upsets of Fisher and Harris, coupled with a GOP victory in Richmond's 3rd Congressional District, means Republicans will continue their tradition of making gains in a state that Democrats once firmly controlled. The GOP now will hold nine of the state's 10 House of Representatives seats. The lone Democratic seat was retained by Southside Virginia Rep. W. C. [Dan] Daniel, a conservative with close ties to area Republicans, who ran uncontested.

Despite cold temperatures and heavy rain, nearly 80 percent of Virginia's voters turned out for yesterday's contest, which many in the state saw as a clear test between liberal and conservative philosophies.

"This was a pocketbook campaign, and people voted their pocketbooks," said GOP State Chairman Alfred B. Cramer."And when you're thinking of your pocketbook, you couldn't vote for the incumbent."

Virinia Democrats were particularly shocked by the twin losses of Fisher and Harris, who had become fixtures on the state scene. Both had survived Carter's loss to Gerald Ford four years ago and Harris had been mentioned as a likely U.S. Senate candidate in 1982.

"They [the voters] wanted to send a message and unfortunately they picked several able-bodied messengers to do it, "said Robb, the state's highest-ranking Democrat.

From the beginning the Carter forces in Virginia were cast in an underdog role, battling a superior GOP machine that gave Gerald Ford his only Southern victory over the former Georgia governor four years ago. Virginians, who have preferred conservative Republicans to moderate or liberal Democrats in almost every major state election of the past decade, had appeared receptive to Reagan's dual themes of less government regulation and a stronger defense policy.

Virginia Democrats were not unaware of their candidate's liabilities. While some Carter supporters claimed late in the race that the president's strategists had targeted Virginia as winnable, others were conceding privately that national Democrats had written the state off. Carter made two brief bill-signing forays to the Washington suburbs and his workers attempted to rally federal workers there by citing the former California governor's calls for a smaller bureaucracy.

Northern Virginia, which Carter had lost by a 52-to-48 percent margin in 1976, was one area where the Democrats hoped to make gains. But Carter failed to make any inroads in the region.

Harris and Fisher faced tough, well-financed challenges from veteran Republican campaigners who realized that the best path to victory was to tie the incumbents to Carter. The incumbents tried to avoid the national ticket and Fisher, in fact, told his workers that he did not want them to distribute Carter literature with his.

While Carter largely avoided extensive campaigning in Virginia, Reagan was much in evidence in the state and in the company of top Republicans. He spend a full day campaigning with them across the state, appeared at a major rally on Sen. John W. Warner's farm and set up his temporary Washington headquarters on a Fauquier County estate adjoining Warner's.

An early GOP poll, taken around the time of the Democratic National Convention in August, showed Reagan in front by a comfortable 12 points. It was a lead that the Carter campaign gradually wore down in September, thanks in part to gaffes by Reagan that left some conservative Virginians troubled.

A Richmond Times-Dispatch poll of registered voters conducted in late September showed Reagan holding only a six-point lead over Carter, with 18 percent undecided.The poll indicated that while Virginians thought Reagan would prove a better doctor for national economic ills by 41 to 30 over Carter, that margin slipped to just 35 to 33 for Reagan when the question was who could best cope with international affairs.

The poll's results caught some of Reagan's more confident supporters by surprise. But they proceeded to raise funds and do the kind of door-to-door, mail and telephone work that has brought Republicans and their conservative sympathizers repeated success in Virginia.

By mid-October, the results of the GOP's groundwork began to emerge. The state party reported raising $201,000 in contributions, much of which was funneled into the Reagan effort -- more than 20 times the $8,000 reported by the poorly organized Democratic Party.

The GOP got another boost when U.S. Sen. Harry F. Byrd Jr., who left the Democratic Party to become an independent, broke a two-generation-old family tradition of silence in presidential campaigns by endorsing Reagan. Democrats scoffed at Byrd's endorsement, saying it would have little impact, but others said Byrd might have pulled many of the state's undecided voters into Reagan's ranks.

Whatever the reason, by late October three separate polls showed Reagan had returned to a comfortable 10-or-more-points margin over Carter. By then GOP leaders such as state party chairman Cramer were confidently predicting victory for Reagan by a substantial margin.

How much last week's Reagan-Carter debate influenced the result was unclear, but a Times-Dispatch poll that had Carter within five points of Reagan in mid-October gave Reagan a solid 12-point edge after the debate -- a margin that held up on election day.

The Northern Virginia races were the only two close ones in the state. Money as well as the advantage of running against an unpopular incubent president favored Parris, who outspent Harris by two to one.