A Virginia legislative committee approved a House redistricting plan today that could radically alter the way most Northern Virginia legislators seek office during the next 10 years.

The plan, passed after four hours of sometimes rancorous debate by the House Privileges and Elections Committee, puts the 18 delegates from Fairfax, Arlington and Prince William counties into l8 separate districts. It is expected to win approval of the full legislature when it reconvenes here Wednesday for another session on redistricting.

For most of the past decade, legislators from Northern Virginia jurisdictions have been elected from large multimember districts that sometimes covered their entire counties. The districts were so large that many legislators complained it was difficult for them to get to know their constitutents and the result was a relatively high turnover among the region's lawmakers.

"It's easier to run in, cheaper to run in and easier for the voters to identify who's representing them," said Fairfax Del. Vincent F. Callahan, a Republican who has represented the county in the 100-member House for 13 years.

Callahan and many Republicans have long argued that the assembly's multimember districts were perpetuated by urban Democrats, chiefly from Norfolk and Richmond. By running on a citywide basis, Democratic legislators from those cities have able to live in predominantly white neighborhoods and still benefit from the large Democratic vote from their cities' black precincts.

The way the legislators drew the lines for the new Northern Virginia House districts today, all 18 incumbents could seek reelection in next year's elections without having to face another incumbent. One opponent of the plan said it could be described as "the work of an amateur helmenthologist worm expert " because of the odd shapes of the new districts.

Fairfax's senior Democratic delegate, Dorothy McDiarmid, was upset today by the proposed change in her county's districts. "I don't think people get as good representation in single-member districts," said McDiarmid, who was first elected to the House in 1960 when Fairfax was represented in Richmond by two delegates.

"Under a single-member plan blacks and women may end up with perhaps a few more elected officials, but with infinitely less power," she said. Proponents of a single-member plan have argued it may increase the numbers of minority legislators by creating urban districts in Norfolk and Richmond that blacks should win easily. The House currently has four black delegates, all from Richmond and Norfolk.

The redistricting bill approved today actually contains two plans. The first, preferred by the committee, retains multimember districts in Norfolk, Richmond, Chesapeake, Hampton, Newport News, Portsmouth, Roanoke and Alexandria. The rest of the state is divided into single-member districts.

The other plan, designated by the committee a "fall-back" option, divides the entire state into 100-single member districts. Under either plan, Fairfax, Arlington, and Prince William counties would be divided into single-member districts. Loudoun County, which has a single delegate representing the entire county, is not affected by the proposal.

Both plans were included in the bill in case the Justice Department or the federal courts have objections to either. In the past both Justice and a federal court have rejected redistricting plans. Republican Gov. John N. Dalton vetoed a third plan.

The House is under a court-imposed deadline of Feb. 1 to resubmit an acceptable redistricting plan its membership. If it fails the court has hinted strongly that it would impose its own redistricting plan, likely a single-member one.

Arlington Del. Elise Heinz sought to include her county's three delegates in their multimember electoral group. Under the preferred plan only cities with populations of 100,000 or more were allowed such districts.

"Arlington is the second most densely populated jurisdiction in the state," said Del. Heinz. "When you're looking at Arlington it is a core city."

Del. Robert Ball (D-Henrico) led the successful opposition to that change. "If we start adopting these amendments for counties, we're going to be right back in the box we were in before Gov. Dalton vetoed our bill." In vetoing the last multimember plan, Dalton said he, too, preferred a single-member plan.

Today's was the 12th public meeting of the House elections committee since last spring when it first met to deal with redrawing the state's political lines to match the 1980 Census. Most of the arguments were familiar. Only the rhetoric changed.

"Abuse of power is no more graceful on the part of legislators than kings," said Richard Turner, chairman of the board of supervisors in rural Isle of Wight County. He opposed joining part of his county with the city of Newport News, which is separated from Isle of Wight by the James River.

Committee members indicated the redistricting bill should have little trouble passing the assembly, but Del. Theodore Morrison (D-Newport News) was philosophical.

"I've long since stopped predicting what the governor will do, the federal courts or the Justice Department," said Morrison. "It's the Christmas season. I hope people will be charitable."