Fresh from her Tuesday victory in which overwhelming absentee voter turnout crushed 11 opponents, Democrat Doris Matsui is scheduled to be sworn into the U.S. House of Representatives Thursday to fill the term of her late husband, Robert T. Matsui.

Matsui left Wednesday for Washington, D.C., planning to take the oath of office about 10:20 a.m. Thursday while joined by 52 other members of California’s congressional delegation. After the formal ceremony, U.S. Rep. Pete Stark, D-Fremont, will introduce her and she will address her 434 colleagues, House officials said.

Matsui, 60, will keep the office of her late husband in the Rayburn office building, said Brian Walsh, spokesman for Rep. Bob Ney, R-Ohio, who oversees House administration.

Robert Matsui, 63, died Jan. 1 of complications from a rare bone barrow disease.

Doris Matsui has promised to support more federal funding for stem cell research in Congress, oppose President Bush’s plan to partially privatize Social Security, support clean energy to reduce greenhouse gas emissions and win funds to expand transit in Sacramento.

Meanwhile, postelection analysis Wednesday revealed that Matsui, a Washington lobbyist and former Clinton White House official, largely won her race before polling places opened Tuesday. Results indicated that absentee voters greatly outnumbered those who actually voted in person — and that 72 percent of them sided with Matsui.

The phenomenon coincided with rising absentee voting statewide, reaching nearly one-third of the votes cast in last year’s primary and general elections, according to the California secretary of state’s office. Statewide, nearly one in five voters now permanently vote absentee.

“When those votes came in, we figured at a 23 percent turnout rate that there was no way mathematically she could lose the race,” said Matsui campaign consultant Jeff Raimundo.

Sacramento County elections officials called it the first time in the county’s history that absentee voters dominated turnout. Fifty-one percent of Tuesday’s voters cast mailed ballots compared to 33 percent who did in last November’s presidential election.

Elections results showed Matsui received 65 percent of the election-day vote and 72 percent of the absentee vote. Amid 24 percent turnout, she won 69 percent of the total vote.

Raimundo said the Matsui campaign did not mount an aggressive absentee ballot campaign, but benefited from its massive use for a one-issue special election.

He said the campaign ran two television advertisements during the weeks when absentee voters began to receive their ballots. One highlighted the need for improved flood control in Sacramento and the other defended the current Social Security system. Both issues were mainstays of her late husband’s campaigns during 26 years representing Sacramento.

Part of the idea was to show she was substantive on the issues, that Doris Matsui was running not as the spouse of a deceased congressman, but as a Washington heavyweight in her own right,” Raimundo said.

Matsui’s extensive TV blitz stemmed from her success in raising nearly $700,000 during the six-week campaign compared to her closest competitor, Democratic activist Julie Padilla, who raised $29,000.

Sacramento County elections official Brad Buyse said the county still has to count “several thousand” absentee votes and provisional ballots, but expects to certify the results by March 18.

Matsui’s swearing-in Thursday will make her California’s third congressional widow since 1998 to assume the seat of her late husband. Voters also elected Santa Barbara-area Democrat Lois Capps to succeed her husband, Walter, who died of a heart attack, and Palm Springs Republican Mary Bono to replace her husband, Sonny, who died in a skiing accident.

Missouri Republican Jo Ann Emerson also assumed the House seat of her husband, Bill, after he died of cancer in 1996.