* Expenses scandal hits Conservatives' support in rural district
* Opposition Liberals resurgent under Trudeau leadership
* Four seats contested in Monday's special election
OTTAWA, Nov 25 (Reuters) - Canadian Prime Minister Stephen Harper's ruling Conservatives only narrowly held onto what had been viewed as a safe seat in a district election on Monday after a scandal over Senate expenses hit his party's support.
The Conservatives' slim margin of victory also underlined the resurgence of the Liberal Party under Justin Trudeau, the 41-year-old son of the flamboyant late prime minister Pierre Elliott Trudeau, who took over the party leadership in April.
The Conservatives' near-defeat in the rural western Canadian province of Manitoba in the special election for the House of Commons will prompt soul-searching in the party, which has held the seat for 56 of the last 60 years, mostly by huge margins.
Harper has been tarnished by a scandal over housing and other expenses claimed by Conservative senators and by an apparent subsequent attempt to cover it up.
The Liberals suffered their worst-ever showing in the last general election in 2011, when they took only fourth place in the Manitoba riding of Brandon-Souris. But under Trudeau, it has catapulted into first place in national polls and came within one percentage point of taking Brandon-Souris on Monday night.
It was one of four districts contested in special elections on Monday, with the Liberals holding on to two they had been defending and the Conservatives keeping two they had held.
In Toronto, Trudeau had handpicked a former Thomson Reuters senior editor, Chrystia Freeland, who was parachuted in to contest a seat vacated by former Liberal interim leader Bob Rae. She beat fellow journalist Linda McQuaig of the left-leaning New Democrats.
Police said last week they believed Harper's former chief of staff, Nigel Wright, was guilty of bribery in corruptly giving C$90,000 ($86,000) of his own funds to a senator to help him pay his expense money back to the government.
Wright says he believes he acted lawfully within the scope of his duties. Harper said no one told him of Wright's payment and he would have vetoed it if he had been told ahead of time.
Trudeau, a former high school teacher and snowboard instructor, has had his share of troubles, but he has managed to maintain some buzz and in Monday's races eclipsed the official opposition New Democrats on his left.
With echoes of U.S. President Barack Obama's campaigns, he has used a slogan of hope and proclaimed his devotion to the middle class despite his wealth and upper-class upbringing.
He took over the left-leaning Liberal Party, which favours more action on tackling climate change, after it took just 34 of 308 seats in the House of Commons in the 2011 election.
The Conservatives, who favour lower taxes and a tough stance on crime, have attacked Trudeau for not having decided on an economic platform, for promoting the legalization of marijuana and for saying he admired China's political system the most of any country outside Canada.
Harper took the unusual step of sending a letter to each voter in Brandon-Souris to point out the dangers of going for Trudeau and many cabinet ministers campaigned in the district.
It was a mixed result for the New Democrats, who had swept into the position of Official Opposition in 2011 in a vote of enthusiasm for the positive spirit of then-leader Jack Layton, who died shortly after the election.
They had no breakthroughs on Monday night, and while they increased their percentage in Toronto, they performed much worse in Brandon-Souris, Manitoba.