Mary Sue Terry, the Democratic candidate for attorney general of Virginia, stands at the blackboard, sizing up a roomful of government students at W.T. Woodson High School in Fairfax County.

It is a tough audience: polite, but not gripped with fascination, on a sunny fall day and right after lunch period, for the state of elective politics in the commonwealth.

No matter. Terry is off -- and running.

"The question I'm asked most frequently is where I'm from," she says. "The second most frequent question is, where's that?"

Where it is is Critz (pronounced Crites), a crossroads in Patrick County on Virginia's rural Southside, a stone's throw from North Carolina.

How small is Critz?

"Critz is so small," she says, "our high school taught sex education and driver ed in the same car."

The room explodes in laughter.

It's a good line -- so good that Terry has been using it in speeches and interviews since at least February, months before she ran off, unopposed, with her party's nomination and a chance to become the first woman elected to statewide office in Virginia history.

After eight years in the state House of Delegates, after loyal service as a protege of Democratic Gov. Charles S. Robb, after amassing a record $1 million in campaign funds and a remarkable coalition of supporters from blacks to conservative white businessmen (even, tacitly, former U.S. Sen. Harry F. Byrd Jr.), Mary Sue Terry leaves little to chance.

"For everything," said her 28-year-old campaign manager, John Jameson, "she prepares."

A Washington Post poll -- sharply criticized by Republicans -- showed last week that she was leading her GOP opponent in the Nov. 5 election, Del. W.R. (Buster) O'Brien of Virginia Beach, 43 percent to 27 percent, with 30 percent of the voters undecided.

"Buster thought he was going to get to run against the woman and she was no problem," said George Stoddart, Robb's press secretary and political adviser. "I don't think he took it as seriously as he needed to. All of a sudden, he found himself $250,000 in the hole."

Terry -- 38, single, a graduate of the University of Virginia law school (classmate: Chuck Robb), practicing lawyer, businesswoman and former assistant prosecutor -- started running for the office two years ago. "I've never underestimated what it was going to take to run a statewide campaign," she said.

Her first fund-raiser brought in $6,000, according to Del. Alson Smith (D-Winchester), a Robb confidant. The second brought in $25,000. A third raised $85,000 and a fourth tapped 52 women for $1,000 apiece. That largesse, and more, helped head off competition for the nomination.

"She has a talent to talk to people and raise money," Smith said admiringly. "It's a God-given talent."

O'Brien, by comparison, had raised $528,112 as of last week.

Seen generally as bright, ambitious, calculating and conservative, Terry's lack of a shrill or strident personal style is credited by many as winning unprecedented support among the state's old-line male conservatives for this particular woman candidate in Virginia. Both Byrd and former governor Mills E. Godwin, the state's two preeminent conservatives, endorsed the top two GOP candidates for governor and lieutenant governor last week, but pointedly stopped short of blessing Terry's opponent, O'Brien.

"The fact that Byrd skipped over Buster in his endorsements tells you he thinks she's the true conservative," said one General Assembly veteran, adding that Terry met privately with Byrd during the last few months.

With few differences between Terry and O'Brien on the issues, the campaign's tone had been genteel until a televised debate a week ago. "It's hard to run against a woman in Virginia," said one senior Democrat in Richmond. "You can call me an SOB, but you can't say that to her."

Asked in an interview before the debate to tick off O'Brien's shortcomings, Terry declined. "Buster's a joy," she said. "Truly."

Then the gloves came off.

In his opening statement of the TV debate, O'Brien zeroed in on Terry's assertion that a four-year stint as an assistant prosecutor in Patrick County, from 1973 to 1977, had given her wide experience and valuable insights into problems of law enforcement.

In fact, charged O'Brien, Terry handled only two jury trials and was limited to dealing with misdemeanors and traffic cases. Terry angrily shot back that she had prosecuted more than 1,000 cases and questioned whether O'Brien's background as a defense lawyer made him fit to be attorney general.

The feud over credentials has grown more heated since.

"Her experience as a prosecutor -- it's an absolute myth, kind of a joke," O'Brien campaign manager Jeff Gregson said in an interview.

Late last week, Terry's campaign manager, Jameson, labeled the charge "at best a reckless one." Jameson said Terry tried "well over 1,000 cases, exclusive of traffic cases," and said the candidate had served as lead prosecutor in at least 14 jury trials.

"Those are the kind of blanket statements we expect to continue hearing from a campaign that's in trouble," Jameson said.

Terry also touts her service on the House's influential, all-lawyer Courts of Justice committee, where she was an early, vocal proponent of tougher drunk-driving laws and of raising the drinking age to 21. She was handpicked by Robb to head his Task Force to Combat Drunk Driving in 1982.

She emphasizes that she has successfully sponsored 65 bills during her legislative tenure while O'Brien sponsored about 18. O'Brien retorts that Terry is able to "shoot a lot of layups" in the House, where the Democrats hold sway.

Judy Goldberg, a lobbyist for the American Civil Liberties Union in Richmond, which does not endorse candidates, disagrees with Terry's stands on such issues as capital punishment (Terry supports it), but credits her with doing her homework.

"She's shown plenty of interest in criminal justice and the whole area of law enforcement, unlike Buster," Goldberg said.

The daughter of schoolteachers who later moved into farm and mill enterprises, Terry is a partner, with her two younger sisters, in the family business. "It's a pure dictatorship run by my father," she joked. "He makes the decisions and my sisters and I make the mortgage payments."

She has not married, she said, "because I haven't met the right person yet."

Her campaign staff downplays the importance of sex and marital status in the race. Those factors become issues in voters' minds, Jameson contended, "when they don't know anything else about a candidate."

Although O'Brien, too, has avoided raising the sex issue on the campaign trail, his aides are less reticent. Answering charges from some Republicans that O'Brien got a slow start as a campaigner, Burden said, "His law practice was sort of a full-time job . . . . He's had a family, different obligations. She's obviously a single-minded woman."

O'Brien's campaign manager, Gregson, maintains he is unconcerned that Terry has outstripped O'Brien in fundraising by a 2-to-1 ratio.

"She needs more money," he said. "She's got to spend more. There are some inherent obstacles she's got to overcome."

Such as?

Gregson laughed. "She's Mary Sue Terry."

Robb's aide, Stoddart, contends, however, that Terry represents a new breed of proud, professional woman that is gaining ground even in a state like Virginia, where male legislators, especially from rural areas, traditionally have written the laws and held the purse strings.

"The brilliance of what she's done," Stoddart said, "is to wed the woman thing" to traditional male power brokers who like her style and support her. "It's womanhood without threat . . . .

"When you take that pride and integrate men who are not threatened by that, you've got a pretty powerful force."