In largely Democratic Alexandria, the sound of falling autumn leaves once was louder than the tepid political debate traditional in races for the city's two House of Delegate seats. Not so this year.

In a special election made necessary by controversy over redistricting, the two Republican challengers have picked apart the records of the city's Democratic incumbents like never before. The Democrats, stung, are trying to make the most of their fledgling seniority and majority party membership and accusing the Republicans of negativism.

"My opponent has a one-year record of raising taxes, increasing spending and trying to hinder our prosecutors in their fight against crime," says Republican challenger Linda Michael, an Old Town architect and political newcomer who is taking on Democratic Del. Marian Van Landingham in the newly created 45th House District in the city's eastern half.

"Democrats in Richmond can wield real clout for Northern Virginia," retorts Van Landingham. "A Republican cannot hope to do the same thing."

"It's been nothing but negativism from Betty," says Democratic Del. Bernard S. Cohen of his opponent, retired legislative aide Elizabeth (Betty) C. McCann, in the 46th House District, which covers the western half of the city and parts of eastern Fairfax County. "She doesn't understand the way the legislature works, and she frequently gets confused."

McCann, making her third bid for the House, has hit Cohen on everything from his attendance record to personal style. "I'm going to retire him," she vows.

The city's Republicans are hoping for a comeback year, after losing one of the delegate seat last November. The Republicans have hammered away at the Democratic incumbents while taking care to emphasize that Northern Virginia Republicanism is closer to Richmond than to President Reagan.

Under the new redistricting, Alexandria is split for the first time into two single-member districts, which are divided by Quaker Lane. The 45th, the eastern district, is about eight miles square and has about 24,000 registered voters. It includes Old Town and the predominantly black, heavily Democratic precincts in the north end of the city -- precincts that have proven immune to annual overtures from Republican candidates.

Van Landingham did well in this part of the city last year. Before her election to the House, she was best known as the driving force behind the conversion of city's Torpedo Factory in Old Town into a center for artists. She was named by the House Democratic leadership as the most effective freshman legislator, and she has a 100 percent rating from the Virginia Women's Political Caucus for her support of the Equal Rights Amendment and other measures.

Republican Michael, the first woman president of the Alexandria Chamber of Commerce, has not run for public office before.

She has accused Van Landingham of being soft on crime, saying she "voted consistently for the defense lawyers ." Michael supports establishment of a crime victim compensation fund that would be supported by fines levied against convicted criminals. Described by the GOP party chairman as being "a feminist and feminine," Michael also supports the ERA.

In the 46th House District, Cohen and McCann are old adversaries.

"Bernie has sponsored nothing but lawyers' bills," McCann says. "He'd be better off retired."

McCann says that Cohen missed almost half the votes on the prestigious Courts of Justice Committee last year. Cohen, who was named outstanding freshman delegate in 1980, counters by saying he has missed less than two hours of House time in more than three years, and that the missed committee votes were part of a subcommittee overscheduling snafu that has been corrected.

"What bills are supposed to come out of a Courts of Justice Committee if not lawyers bills," replies Cohen.

The 46th has about 22,000 registered voters and includes the large number of condominiums in the Landmark area -- known as Condo Canyon -- and neighborhoods of single-family homes. It stretches west to envelope the Park Lawn precinct of Fairfax County. The district generally is thought to be more Republican than the 45th, though the transient character of its neighborhoods, and the fact that Virginia voters do not register by party, make voter behavior difficult to predict.

McCann says her experience as a legislative aide for longtime Northern Virginia Rep. Joel T. Broyhill makes her an ideal choice in an era of declining federal subsidies. She favors elimination of the sales tax on food, and says she, unlike Cohen, has time to travel all around the state on Alexandria's business.