From left, Ginny Peters, Viki Kinsman, Henry Rackowski and Ed Caughlan doublecheck votes from Election Day in an official "canvass" on Nov. 9. (Katherine Shaver/The Washington Post)

Fairfax County elections officials said Saturday that they had discovered about 3,200 absentee ballots that went uncounted on Election Day, producing a chunk of new votes for Democratic state Sen. Mark R. Herring in the still-undecided race for Virginia attorney general.

The newly found ballots added another twist to the closely watched contest for the commonwealth’s chief lawyer that will likely end in a state-funded recount in December. The high stakes were underscored by the dozens of operatives from both parties who descended on the Fairfax County Government Center to monitor the election board’s proceedings.

The winner will hold an office that has become a launchpad to the governorship and national politics.

Virginia Republicans, who narrowly lost the governorship and lieutenant governor’s posts to Democrats on Tuesday, are hoping to avoid being shut out of statewide office — including both U.S. Senate seats — for the first time since 1970. Democrats are eager to secure a post that has not been held by the party since 1994.

The number of uncounted ballots in large, heavily Democratic Fairfax, more than officials had initially believed, yielded 2,070 additional votes for Herring (D-Loudoun) and 938 for state Sen. Mark D. Obenshain (R-Harrisonburg). Some ballots contained write-in candidates for attorney general.

On Saturday evening, the Virginia Board of Elections updated the statewide tally to show Obenshain ahead by 55 votes of the 2.2 million cast. The margin is expected to remain a moving target — shifting as corrected counts flow in from local election boards — until the canvassing deadline of midnight Tuesday.

Meanwhile, Fairfax elections officials said they were caught off guard Friday when the state Board of Elections issued instructions that changed local procedures for considering the provisional ballots of those who voted on Election Day but, for some reason, hadn’t appeared on regular voter rolls. These include, for example, people who voted absentee overseas in previous elections and had since returned to Virginia, not realizing that they were still considered absentee, officials said.

The state Board of Elections ruled Friday that those who want to argue for their provisional vote to be counted have to appear in person before the local Electoral Board. Officials said they issued the directive to ensure that procedures for evaluating provisional ballots were uniform across all counties.

Fairfax officials said their practice had been to allow provisional voters to designate party officials as their legal representatives. Democrats said they were disproportionately hurt by the change, given the county’s partisan makeup. They also questioned the timing of the directive, issued 72 hours after a race that ended in a virtual dead heat.

“The real question for everybody here is whether or not that change makes a difference and whose vote is counted,” said Terry Adams, a member of the Mason District Democratic Committee.

In a close contest, Adams said, “it could make a big difference.”

Adams said the Fairfax Democratic Party called provisional voters Friday night to urge them to appear in person Saturday before the county Board of Elections, as it began to consider which provisional ballots to count.

By noon, however, just over 20 people out of the 493 who had cast provisional ballots had appeared at the Fairfax County Government Center, officials said. The board will continue to consider those ballots and hear from voters until 1 p.m. Tuesday, officials said.

The counties must certify their election results by midnight Tuesday. The state Board of Elections will conduct its own review and certify state results by Nov. 25. The losing candidate in any race that ends with less than a half-percent gap can request a recount at state expense.

In the tight race, many eyes remain on Fairfax and its outsize impact on statewide elections.

“It’s going to be awfully close,” said George Burke, a spokesman for Rep. Gerald E. Connolly (Va.) and a Democratic Party activist.

“It’s very, very, very close,” said Jay McConville, chairman of the Fairfax County Republican Committee, “and the numbers keep changing.”

Brian W. Schoeneman, secretary of the Fairfax County electoral board, said staff traced the miscount to “simple human error” and a broken machine for 8th Congressional District voters at the Mason Government Center in Annandale. It had been used by those voting absentee in person before Election Day. Absentee votes are not counted until 7 p.m. on Election Day, officials said.

On election night, officials re­scanned all the ballots from the Mason center using a functioning machine. That tally also included absentee ballots that had been mailed in. The machine spit out a paper tape showing the correct tally of 2,688 voters, Schoeneman said.

However, election officials mistakenly used another tape with results from only 710 voters — results wrongly reported Tuesday night.

“This is simply an error that happened to be magnified by the closeness of the A.G.’s race,” Schoeneman said.

County elections officials also found 342 other absentee votes that had been left out because of “math errors,” he said.

“We know this is a very critical race, and everyone is paying very close attention,” he said.