Democrat Mark Herring, left, and Republican Mark Obenshain participate in an October campaign debate during the Virginia attorney general race. (Jahi Chikwendiu/Washington Post)

Democrat Mark R. Herring continued to widen his slim lead over Republican Mark D. Obenshain in the race for Virginia attorney general Tuesday as the recount of the historically close contest spread statewide.

Herring’s lead grew to more than 810 votes, with 73 percent of ballots across the state recounted, according to Herring’s campaign.

Fewer than 120 ballots had been “challenged,” the campaign said, meaning recount officials could not agree on how they should be counted and will forward them to a special recount court in Richmond that will begin its work Wednesday.

The Democrat’s lead was between 811 and 866, depending on how many of the challenged ballots are ultimately counted, Herring attorney Marc Elias said in a conference call with reporters. Herring’s lead is the larger number if all of the challenges are overturned, the smaller one if they are all upheld.

“We continue to gain margin at a steady pace, and we expect to continue to do so through the rest of the day and through the rest of the recount,” Elias said. “We remain confident that Mark Herring will be declared the winner of the recount.”

It is not clear what Obenshain will choose to do if, at the end of the recount, Herring leads by more votes than there are challenged ballots.

“This is an ongoing process,” said Obenshain spokesman Paul Logan. “It’s important to see it through and ensure that we get an accurate result. That’s been our goal since the minute polls closed.”

Both campaigns dispatched legions of volunteers to courthouses across the state. Herring’s campaign issued updated tallies throughout the day through conference calls with reporters and Twitter. Obenshain’s campaign did not announce running tallies, but it did not publicly take issue with those provided by the opposing campaign.

The race to succeed Attorney General Ken Cuccinelli II (R) has turned into a protracted nail-biter, one that will not only determine who serves as Virginia’s top law-enforcement official but also could shift control of the evenly split state Senate.

Herring and Obenshain are both senators, and an election would be held to replace whichever one becomes attorney general. Because Obenshain hails from reliably conservative Harrisonburg and Herring from battleground Loudoun County, a win by Herring could cause the Democrats to lose sway in the Capitol. The GOP has a wide margin in the House.

If the 800-vote lead holds, the race will lose its distinction as the closest statewide election in Virginia history. At least initially, the attorney general’s race appeared to knock out the current record-holder, the 2005 contest for attorney general between then-Del. Robert F. McDonnell and Sen. R. Creigh Deeds (D-Bath). McDonnell won that race by 360 votes.

The State Board of Elections declared Herring the winner by just 165 votes out of more than 2.2 million cast, a margin so slim it entitled Obenshain to a government-funded recount.

Elections officials in three jurisdictions got a head start on their recounts Monday — Fairfax County because of its large size, and Alexandria and Chesapeake because their voting machines required them to recount by hand. Their counterparts across the state began Tuesday. All of them have through Wednesday — the deadline for some localities is as late as 11:59 p.m. — to recount their ballots.

All jurisdictions will send their challenged ballots to be reviewed by a three-judge panel in Richmond, which will also hear any disputes between the two campaigns.

The court will meet Wednesday, Thursday and possibly Friday, and it is expected to announce its result by Friday. Under Virginia law, the loser can contest the result in an unusual joint session of the General Assembly but must do so by Monday.

Arlington County began its recount Tuesday morning and was done by 11 a.m., according to a Twitter feed from the county elections office. Herring added two more votes to his lead there, and there was one challenged ballot. In Loudoun, according to county spokeswoman Anna Nissinen, Herring had a net gain of 62 votes, and two ballots were challenged.

After a day and a half of recounting Alexandria’s votes by hand, Registrar Tom Parkins said that both candidates finished with six more votes. Herring now has 30,285 votes there, and Obenshain 10,429. Two challenged ballots are being sent to Richmond.

“For all the concern about the lack of our system’s ability to count accurately, this shows it is extremely accurate,” Parkins said.

Republicans have raised questions about how Fairfax, the state’s largest jurisdiction, handled some ballots — complaints that could lay the groundwork for asking the General Assembly to decide the election or call a new one. That sort of challenge, allowed under a little-known state law, would have to be premised on claims that the election was deeply flawed.

Obenshain’s attorney, William H. Hurd, said in court last week that the Republican “may wish to consider that possibility,” but he later called talk of a contest “premature” and “hypothetical.”

Obenshain’s campaign has complained about how Fairfax handled provisional ballots, which are used when voters lack identification or show up at the wrong polling place.

Some provisional voters in the heavily Democratic county got four extra days than those elsewhere in the state to appear in person to argue that their ballots should be counted. Obenshain’s campaign has said the extra time was unfair to voters elsewhere, but the board said it acted legally.

Obenshain’s campaign also said this month that Fairfax officials misplaced some used ballots and blank ballots after the election, belatedly turning them in to the Circuit Court clerk. Brian W. Schoeneman, secretary of Fairfax County’s Board of Elections, has confirmed that account but said the ballots, although misplaced, had been securely stored in a locked cart with voting machines.

Schoeneman said mistakes on election night are bound to be discovered because “this is a human process” and “there is no such thing as an error-free election.”

For example, he said, in the county’s Cameron Glen precinct, officials learned that the sign-in sheet on election night had 13 more voters than votes counted. Herring gained eight of those votes and Obenshain gained five, according to a running tally posted on a dry-erase board near the Jury Assembly Room, where most the recounting was being done.

“I would expect there’s going to be one or two more [such cases] here and there,” Schoeneman said.

“Unfortunately, given the size of Fairfax County and the closeness of this race, that may have an impact,” he said. “But it’s too early to tell, at this point, what that impact may be.”

Patricia Sullivan contributed to this report.