With Northern Virginia Democrats only a few days away from the first round in choosing their nominee for the 8th congressional seat, candidates Les Fettig is not exactly radiating optimism.

"Anybody has a chance," said Fettig, a former Carter Administration official who is challenging incumbent Rep. Herbert E. Harris. "Sure, I'm an underdog -- but then, the Jets beat the Colts in the first Superbowl."

If Fettig is realistic about his chances of capturing enough delegates to win the nomination, he is by no means serene. As far as Fettig is concerned, he is the victom of a political fix.

Fettig, a relative newcomer to Virginia politics, wanted to challenge Harris in a primary. Last month, however, the 8th District Democratic Committee voted to choose the party's nominee through a mass meeting-convention process.

That process opens with eight mass meetings to choose representatives for a districtwide meeting May 10, when party members will choose a nominee for the congressional seat and five delegates to the Democratic National Convention in New York City. The mass meetings begin Monday in Alexandria and include April 12 in Manassas City.

"The American political system is collapsing and this is good evidence of why," said Fettig, who publicly branded the district committee dicisions as "back-room maneuvers" designed to benefit Harris.

But Ray Colley, chairman of the district committee, said the decision was made because a convention is less expensive, more convenient and not as divisive as a primary.

"Both primaries and conventions are used, have been used and will be used," said Colley last week. "The people who have to make the decisions made them."

If Fettig was upset by the rejection of a primary, he was outraged when the committee cut his campaign time by more than a month. Two weeks ago the committee voted 7-6 to hold the mass meetings on May 10. Eight days later, the committee reversed itself and rescheduled the meetings for the first two weeks of April.

"No wonder people are disgusted with politics," said Fettig, who protested the change to the state Democratic committee. after his appeal was rejected, he complained again that the 8th District committee was dealing a pat hand to Harris.

Colley defended the change in dates. He received many complaints about the original decision to select the congressional delegates on the same day presidential delegates to be picked at the 8th District convention. It would be inconvenient, said Colley, for Democrats to spend an entire day choosing delegates.

"He (Fettig) should get going on his campaign and quit complaining," said Colley.

Harris denies that the committee acted on his orders, but he does say it would be "naive" to suppose that he didn't have "broad support" on that committee.

"I sent a letter to the committee, indicating that this was strictly the committee's choice and I would support anything they decided to do."

While the Democrats squabble, the Republicans in the 8th District, which encompasses the southern half of Fairfax County, Alexandria, Prince William County and northern Stafford County, are showing little sympathy. Republicans will nominate their candidates in a primary election June 10.

"For 15 years we have been criticized for choosing our candidates in a smoke-filled room. Now it's a convenient mode of nomination," said Stanford E. Paris, one of two candidates for the Republican nomination. "It's politics as usual for the Democrats."

Parris is seeking to recapture the seat he lost to Harris six years ago. Before that upset, Parris had served two terms in Congress. He now heads a liaison office on Capitol Hill, representing the State of Virginia in dealings with Congress.

Parris, a Fairfax County lawyer, comes to the campaign with a long record of political service. He was a member of the county Board of Supervisors from 1964 to 1967 and served in the Virginia House of Delegates from 1969 until 1972.

Parris' opponent for the nomination will be Robert L. Thoburn, the owner and director of a Christian school in Fairfax County.

Thoburn, a conservative who was defeated last fall when he ran for reelection to the House of Delegates, has sought the 8th District congressional seat twice before. Two years ago he placed third in the Republican primary, behind Fairfax County Board Chairman John F. Herrity, who went on to lose in a bitter campaign against Harris.

Republican regulars say Parris is the stronger of the two candidates within the party, but Thoburn's name recognition from current campaigns could be a decisive advantage in a primary. Thoburn also has benefitted in the past from the contributions of national conservative organizations.

Then there is the Democratic crossover factor.

"With their nominating process behind them, Democrats will be free to do whatever they like. Virginia voters don't register by party," said Parris. He said he fears Democrats may vote for the more conservative Thoburn because they think he would be a weaker candidate against Harris. "There is ample opportunity for that kind of mischief."

That same concern among Democrats wary of Republican interference helped the 8th District committee decide on a convention rather than a primary this year, according to Harris' campaign coordinator, Joseph Wisniewski.

Wisniewski said there is nothing "untoward, different or back-room" about the convention method, and he doesn't believe Fettig's complaints will hurt Harris, either at the mass meetings or during the general election. What Wisniewski believes will hurt Fettig, however, is his admission that he voted for Herrity, Harris' Republican opponent, in 1978.

"Certainly a die-hard party worker would look at that and wonder, 'where is this young fella coming from?'"

Fettig says the only Republican vote he ever cast occurred before he officially became involved in Democratic party politics, but after the "treatment" he received in his nomination bid, Fettig hints that he may begin looking for "another option."

"These actions really bring into question the integrity of the whole Democratic Party. It's a very unpleasant set of events," said Fettig.