Republicans on the Fairfax County Board of Supervisors, with their leader accusing state Democrats of "shabby Chicago-style politics," yesterday carried a 5-to-4 vote to redistrict the county, defying a Virginia General Assembly bill that would prohibit redistricting until 1991.

With board Chairman John F. Herrity, a Republican, leading the charge, the board set a series of private and public hearings that will climax with the realignment of the county's eight political districts by July 1.

The move placed the county on a collision course with the state legislature, which just last week adopted legislation that would prevent Fairfax County and other local jurisdictions throughout Virginia from redrawing political district lines until 1991.

County governments in Virginia are required to reapportion district boundaries every 10 years. Before last week's vote in Richmond, those local governments were permitted to redraw district map lines more frequently if they wished.

The state bill, scheduled to take effect July 1, was made retroactive to Jan. 1 to block any countermoves, such as the one initiated yesterday by Fairfax County. But Herrity vowed to proceed with the redistricting and to take the fight to court if necessary.

Herrity said the state bill was the product of "shabby Chicago-style politics" carried out by Democratic state legislators intent on protecting the seats of the board's Democratic minority. He charged that the state Democratic Party, which he said controls Virginia "from the courthouse to the statehouse," is violating the home rule rights of local jurisdictions.

In dissenting remarks, Supervisor James M. Scott (D-Providence) warned of the "disruptive" and "divisive" effects of any redistricting plan and ridiculed Herrity's comments lamenting the state bill as a threat to democracy.

"I don't believe democracy requires Fairfax County to redistrict every five years," Scott said.

Other Democratic board members claimed that the board's Republicans were using population inequities as an excuse to increase their one-seat majority on the county's governing panel.

"It's to strengthen (T.) Farrell Egge (R-Mount Vernon) and to give Jim Scott the squeeze," board Vice Chairman Martha V. Pennino (D-Vienna) declared shortly after the vote. "There is no question in my mind that the whole issue is political from beginning to end."

Political observers have said that Scott, a four-term supervisor who has never won with more than 53 percent of the vote, is the most vulnerable Democrat in the 1987 county elections and thus would be a prime target of any redistricting effort.

In defense of their plan, the Republicans have repeatedly pointed out that the board, when under Democratic control, carried out similar moves both in 1965 and in 1975. The Republicans have charged that criticism from some of the same Democrats who participated in those earlier efforts amounts to hypocrisy.

Supervisor Thomas M. Davis III (R-Mason) said redistricting at the halfway point between each 10-year census is "a time-honored county tradition" employed to address population shifts spurred by rapid growth. He called objections by board Democrats "convoluted."

At the same time, Davis sought to allay concern among Democrats that a remapping would cause them political harm. "The fears of a partisan gerrymandering are essentially groundless," he said.

That theme was picked up by Supervisor Nancy K. Falck (R-Dranesville), who said her Democratic counterparts were prepared to "surrender home rule" because of unsubstantiated alarm about their political status.

Turning to longtime adversary Audrey Moore (D-Annandale), Falck said that Moore opposed remapping attempts even during the mandated redistricting to address new census figures in 1981.

"You were running around and saying the sky was falling in and people were out to get you" then, Falck said.

Moore, joining with her Democratic colleagues in opposing the move, contended that the Republican effort carried a "partisan flavor" that was absent during the Democratic-led redistricting in 1975.

Herrity, however, singled out politics as the sole motive of state assembly members who supported the bill limiting the county's redistricting powers.

"Why is the 1986 redistricting being opposed in Richmond when the 1975 redistricting caused not a flicker of interest in Richmond?" Herrity asked. "The answer is blatant, arrogant politics. In 1975, Democrats outnumbered Republicans on the Board of Supervisors 8 to 1. In 1986 the Democrats are outnumbered on the board 5 to 4. But they are not outnumbered in Richmond. "In Richmond, they control the votes to change the rules."

Under a tentative schedule released yesterday by Herrity, the board will entertain redistricting proposals from the general public until April 7 and hold a public hearing on April 21. A vote on a redistricting plan was set for April 28.