Normally, Mary Margaret Whipple might spend her few spare moments deep in an Agatha Christie or Dorothy Sayers mystery. Or you might find her with her family in their North Arlington home cheering for the Redskins.

But these are unusual times for the 41-year-old Whipple, a Democrat who is waging a vigorous campaign to unseat Stephen H. Detwiler from his at-large seat on the Arlington County Board. Detwiler, currently chairman of the board, is a Republican-endorsed independent.

Whipple's hectic schedule of staff meetings, debates and neighborhood "coffees" has left her little time for the Redskins, and her reading list -- top-heavy with official documents on county issues -- is not likely to have the zing or the surprise endings of her favorite mysteries.

But there's no guessing about how Whipple would write the finale of her campaign story: a victory that would give Democrats the control of the five-member county board that they lost four years ago.

The Whipple-Detwiler contest has proved to be one of the liveliest county board campaigns in recent years, with both candidates trading heated barbs on issues ranging from the economy to the question of open government in Arlington County.

Detwiler has accused Whipple aides of running a "negative, deceptive campaign." Whipple counters that since she is "addressing Detwiler's record and he calls it negative, then I think you have to take his word for it."

At the same time, Whipple has been critical of past support for Detwiler from the National Conservative Political Action Committee (NCPAC). In the records of his 1978 campaign for the county board, Detwiler listed a $500 contribution from NCPAC, and Whipple says she finds it "disturbing" that a national conservative group could influence a local campaign. Detwiler says he didn't solicit the NCPAC contribution and hasn't received any funds from NCPAC in this campaign.

Whipple, a transplanted Texan, is making her second bid for the county board. Three years ago, she came in a close third behind two GOP-backed independents, Walter L. Frankland and Dorothy T. Grotos. This year, Whipple and her advisers are targeting several traditionally Democratic precincts scattered throughout the county. With a neighborhood blitz to register as many party supporters as possible, Whipple and her staff hope to get a large Democratic turnout in a county where Democratic voters generally are acknowledged to outnumber Republicans.

Whipple grew up in College Station, Tex., where her father was a professor at Texas A & M University and her mother taught in the public schools. She spent two years at Rice University in Houston, where she met her husband Tom. The Whipples moved to Arlington shortly after they married. Whipple completed her undergraduate degree in English literature at the American University and earned a master's degree in American studies at George Washington University.

She has worked as an editor at the former U.S. Office of Education and taught English for five years at Northern Virginia Community College. The Whipples have two daughters, Beth, a freshman at George Mason University, and Margie, a junior at Yorktown High School.

Although Whipple moved to Arlington 22 years ago, she has not entirely abandoned her Texas roots. In a sentimental holdover from those days, she has adopted the maroon-and-white colors of her high school and Texas A & M for her campaign.

Whipple describes herself as "moderate to liberal on social issues, but a fiscal conservative."

In Arlington, Whipple is best known for her work on the county school board, where she served from 1976 to 1980, including one year as chairman. Whipple came to the board through her involvement with the Arlington chapter of the American Association of University Women. In 1973, she was the AAUW appointee to a special school board committee. Later, after heading a group to map out long-range educational goals, Whipple was encouraged by some Democratic members of the county board to seek a school board seat.

In her last campaign for county board, Whipple may have been a victim of a conservative shift among county voters, according to her campaign manager, Lucy Denney, who also managed the 1979 campaign.

"In 1978, people thought it was time for a change," Denney said. "There was some dissatisfaction with the Democrats. Now, I think, they've had enough of the Republicans."

Some observers believe Whipple also will be able to capitalize on a Democratic organization that has helped elect two party-supported candidates -- Ellen M. Bozman and John G. Milliken -- to the county board in the last two years. Whipple also has the endorsement of Arlingtonians for a Better County, a self-described nonpartisan organization, which often has backed Democratic-supported candidates.

The Whipple campaign hopes to raise about $35,000, Denney said, mostly for mass mailings to county voters, although some funds may be used for radio ads. So far, Denney estimates, the campaign has raised $19,000 to $20,000, much of it in small donations from between 500 and 600 supporters.

Whipple said the major reasons she decided to run this year are her differences with Detwiler concerning schools, economic development and what she calls the need to restore "open government" to Arlington.

She is particularly critical of what she says are "artificially low" spending guidelines for the schools set by the GOP majority on the county board. Last year, she said, those spending guidelines resulted in $1 million in instructional cuts, forcing the school system to lay off teachers and aides.

Whipple contends that the GOP majority has displayed "an unwillingness to recognize the changes in the population in the schools and that the schools must adapt and provide for the needs of all different kinds of students who are coming in."

Whipple also has taken a hard line on what she calls the "need to restore open government to Arlington." Two prime examples of "closed-door" government, Whipple says, are the appointment of school board member Simone J. (Sim) Pace and the firing of former county manager W. Vernon Ford.

Whipple said she was upset when it was disclosed that Pace, a Republican, would be the choice for a school board vacancy last year -- a disclosure made before the deadline for candidates' applications had expired.

And although she does not contest the county board's right to fire its county manager, Whipple has been sharply critical of the way the Ford dismissal was handled:

"Mr. Detwiler told Mr. Ford to resign or be fired without [Detwiler's] having properly called for an executive session of the full county board or having an evaluation of Ford within the past year," she said. Detwiler did not consult the board's two Democrats before his private session with Ford, she noted.

Whipple and Detwiler also have clashed on economic development, with Whipple arguing that the board should be more cautious in giving developers "bonus density credits," a trade-off in which the developer is allowed greater building densities than normally permitted in exchange for providing other amenities, such as a park or sewer and road improvements.

Although Whipple believes the credits are "a legitimate strategy" for getting concessions beneficial to the community, she said "they need to be used much more carefully and for the good of the community."

Whipple also supports a proposal to create a local housing authority as a "promising way to rehabilitate garden apartments and maintain them as rental properties." The county board, she added, could maintain some controls over the authority.

She is opposed to a proposed regulation that would bar children under 16 from business establishments, particularly those with video-game parlors, during school hours and between midnight and 5 a.m. Such a law, she said, would be "an interference in family life and intrusion on parental responsibilities . . . [and would place] an undue burden on businessmen to enforce it."

Whipple is an admirer of novelist Upton Sinclair, best known for one of his early books, "The Jungle," which was an indictment of the cruel working conditions in the meatpacking industry in the early part of this century. Sinclair, who ran for governor of California three times, wasn't afraid to put down his pen and get actively involved in the political issues of his time, Whipple said.

"I was fascinated with somebody like Sinclair who got very involved in politics," Whipple said. "He was an interesting combination of someone who was a writer, but instead of someone writing pure fiction he was really commenting on his time."