If the opening volleys in the race for Virginia's 8th Congressional District seat harbour any omens, then campaign watchers might do well to take a cue from. Bette Davis' advice in All About Eve. "Hang on to your hats, fellas," says the lady at one point in the movie. "It's going to be a bumpy ride."

It began with a congratulatory telegram from Rep. Herbert E. Harris to Republican primary winner John F. Herrity. Harris' missive combined a proposal for a series of debates (to take place after the House adjourns Sept. 29) with a brief lecture on the democratic process.

After asking Herrity to join him in signing a "fair campaign practices pledge," Harris asked his opponent to "focus your campaign on a positive discussion of the issues. A negative-oriented campaign that misrepresents and distorts a candidate's record has no place in Virginia's electoral politics."

Harris then went on to advise Herrity that "an effective campaign can and should be run within the bounds of human and political decency," and that by doing so Herrity could "help the faith of Northern Virginia voters in politicians and the political process."

In response, Herrity fired off an equally wordy if somewhat less flowery telegram of his own. "Your proposal to start campaigning on Sept. 29 is a copout," Herrity said. "The campaign starts today, June 14. I will accept every possible invitation for joint appearances from responsible groups, whether you see fit to campaign from the 'Rose Garden' or before the people."

Herrity did agree to sign a fair campaign practices pledge, but said that he failed "to see any validity to (Harris) promise of undistorted and honest presentation of the records and the issues." Herrity also told Harris that he thought Harris' "missionary efforts for fair and honest representation of records and issues should begin in (his) own office."

Such zippy dialogue is an old refrain in the Harris-Herrity antagonism, which began back in the days when both men sat on the Fairfax County Board of Supervisors and began a relationship that seemed to owe a lot to the mongoose-cobra school of political enmity.

This was back in the days when Harris was part of the Democratic majority that made the board decisions on county affairs with little help from either mavericks like Audrey Moore (D-Annandale) or a lone Republican like Jack Herrity who came to the board in 1972 with little political power and even less politesse.

Harris glossy self-confidence was a source of constant irritation to the rough-hewn Herrity, say those who observed the two at that time. Moreover, the way in which the majority, often led by Harris, pushed through its decisions with only a rare regard for his presence apparently galled Herrity even more deeply.

Direct competition and confrontation between the two men ended, however, when Harris won his congressional seat in 1974. Herrity went off to score an upset victory for the county board chairmanship over incumbent Democrat Jean Packard in 1975 and now presides over and paticipates in the fractious and often shifting coalitions of the three loosely knit factions of the nine-member board.

But Herrity's and Harris many differences have not prevented them from racing for some of the same political high ground on the issues. The incessant ballyhoo over the "taxpayers" revolt" and the shadow of Proposition 13, the California referendum that drastically cuts that state's property taxes, will make a dramatic mark on the 8th District election, both men believe, and each of them is claiming its benefits for his own.

"I feel (Proposition 13) was a manifestation of an attitude growing throughout the country," Harris said recently. "What it was saying loud and clear is that the property tax is placing an unfair burden on the average citizen, and we've either got to cut spending or redistribute the tax burden."

Herrity also sees Proposition 13 as "indicative of a mood" shared by the voters of the 8th District and one that will work in his favor. Throughout the primary campaign, Herrity tried to draw a dramatic contrast between his own economic policies and his portrait of Harris as a "big spending liberal."

Harris, meanwhile, has been emphasizing his own proposals for cutting the federal budget and notes that "anyone who can't come up with a specific program for reforming the property tax laws is going to have a lot of explaining to do in this campaign."

Unlike some election years where the voters' attention is divided between campaigns for everything from president to prom queen, there are only two major races of interest to the 8th District this fall - the congressional seat and the statewide Senate race between Republican Richard Obenshain and Democrat Andrew Miller. This time around, observers say, there should be little that will obscure the candidates and their stands on the issues.

It may be a while, however, before both candidates meet head on. Besides attending a splashy $125-a-plate fundraiser billed as "an evening with Vice President Mondale," scheduled for tonight, Harris plans to act more like a congressman than a candidates until the recess. Herrity, meanwhile, is already embarked on his door-to-door campaign. But despite the wide gulf between the two men's styles and their stands on the issues, they do share a talent for self-promotion that should keep the campaign from drowning in the tepid waters of the kind of "gentlemen's agreements" that took the zest out of the primary campaign.