Virginia House Speaker A.L. Philpott, a crusty Southside Democrat and chief of the state's old-line rural politicians, traveled several hundred miles north to put in a cameo appearance Sunday at a fund-raiser for Phil Chabot, a first-time candidate for the legislature from Fairfax County.

Meanwhile, Attorney General Gerald L. Baliles was the featured guest at the house of Del. Nora Squyres, the Democratic incumbent from the Annandale area. He and other ranking party leaders later turned up at a "chocaholics" party (featuring several dozen types of chocolates) for Alexandria's two incumbent Democratic delegates.

The same day the legislature's two majority leaders, Sen. Hunter B. Andrews of Hampton and Del. Thomas Moss of Norfolk, hosted a brunch at a West Springfield restaurant for 28 Democratic candidates, before rushing to a function for the party's candidate for commonwealth's attorney in Arlington.

By Sunday evening, as Fairfax County Democrats gathered on the banks of the Potomac for their campaign kickoff, the traveling troupe of Democratic politicos had grown to include the lieutenant governor, the chairman of the House Democratic Caucus, the chairman of the House Appropriations Committee and one of Virginia's prominent women legislators.

For a region that has at times been made to feel like the stepchild of the Old Dominion, Northern Virginia is witnessing quite an array of downstate political muscle.

The ostensible reason for the invasion is the fall's political campaigns.

This year, like other years, there are more contested legislative races in Northern Virginia than anywhere else. Legislative elections are already over in Norfolk: none of the five Democrats there face any opposition Nov. 8.

That explains why Moss was available for last weekend's whirlwind tour. This fall, he said, is the first he can remember being free at election time.

Philpott's presence was more exceptional. He said he came because some of Chabot's classmates at the University of Virginia law school are also his friends and they "lit some firecrackers to get me up here." According to another ranking Democrat, Philpott came because Chabot asked him. "He said no one up here ever asked him before," the Democrat said.

The novelty is not just that downstate Democrats are willing to come en masse to pay their respects to Northern Virginia, but that local candidates are eager to have them.

Emilie Miller, Democratic candidate to succeed retiring Sen. Adelard L. Brault in Fairfax, said she hopes endorsements and appearances by people like Andrews and Moss will undercut the argument that, as a woman, she won't win respect in Richmond's "good ol' boy" network.

Behind the surge in party spirit, other motives are at work.

Lt. Gov. Richard J. Davis, Baliles, House Appropriations Chairman Richard Bagley (D-Hampton) and Senate Majority Leader Andrews have ambitions of their own, mostly centered on the 1985 gubernatorial elections. (Andrews is still "considering" a run for the U.S. Senate next year.)

And they're drawn to Northern Virginia's traditional political events for the same reasons that Del. Mary Sue Terry (D-Henry), mentioned as a possible candidate for attorney general in 1985, and former delegate Edythe Harrison of Norfolk, who's already running for the U.S. Senate, showed up at the Sunday party--to get to know and be known by the party faithful.

There was irony, however, in seeing downstate Democrats--many of whom grew up in what was virtually a one-party state--come north to give partisan pep talks.

That was a point made by retiring Republican Del. Warren Barry, a candidate for clerk of Fairfax County Circuit Court, who showed up at one Democratic function in comic disguise.

"It certainly is great to see Tom Moss and Hunter Andrews, who have combined 40 years of experience and never had any real Republican opposition, come up here from Norfolk and Hampton to tell you up here how to run against Republicans," Barry quipped.