* Liberal debate showcases crowded field
* Rival asks: 'Where's your plan?'
* Analyst says Trudeau is still the one to beat (Updates with comment from analyst)
By Russ Blinch
Jan 20 (Reuters) - The race to find a new head of Canada's minority Liberal Party is about ushering in someone with "vibrant ideas" who can help the struggling middle class, Justin Trudeau, the son of charismatic former Canadian leader Pierre Trudeau, said on Sunday.
The younger Trudeau, lauded for his charisma as much as he is criticized for lacking substance, is part of a crowded field of nine candidates vying to bring the once dominant party out of the political wilderness. He is a member of Parliament from a Montreal district.
"For the first time, this is about bringing forth a new generation of leadership with bold ideas, with strength and vision," Trudeau said in Vancouver, British Columbia, in the first of a series of leadership debates.
Trudeau is seeking to recreate the excitement that surrounded his father when he was first elected in 1968, with the ultimate aim of unseating the Conservative government of Stephen Harper, which won a majority in 2011.
With an army of followers on Twitter, Trudeau is the front-runner in the race to head a party that has shrunk to third place in Parliament for the first time in its 145-year history.
Trudeau, like his late father, stands for a united Canada and is a foe of separatist forces that have dogged politics in his home province of Quebec. The separatist Parti Quebecois was returned to power in a narrow provincial victory late last year.
Marc Garneau, a former Canadian astronaut and member of Parliament, spoke of protecting the environment, saying he had been around Earth hundreds of times and knew something about protecting the planet.
"This leadership race must be about new ideas," said Garneau, seen as a possible challenger to Trudeau's front-runner status.
The candidates generally expressed strong support for the middle class and affordable housing, while accusing the Conservative government of disregarding the environment in its bid to exploit the massive oil sands resources in Western Canada.
Joyce Murray, a member of Parliament from Vancouver, pressed Trudeau as he discussed ways to oust the prime minister.
"If you want to replace Stephen Harper, where is your plan?" Murray asked Trudeau in a direct exchange.
Alex Sevigny, a political analyst at McMaster University in Hamilton, Ontario, said after Sunday's performance, Trudeau was still the one to beat.
"Justin Trudeau didn't make any errors tonight and spoke with confidence and authority," Sevigny said. "His position as front-runner has not been affected."
Trudeau, a former school teacher who is married with two children, is often criticized as running on his name, which carries the same dynastic weight in Canada as Kennedy or Bush in the United States.
The Liberals governed Canada for nearly 69 years in the 20th century, but were won only 19 percent of the popular vote in the 2011 election. (Editing by Cynthia Osterman and Christopher Wilson)