* Justin Trudeau becomes Liberal leadership front-runner
* Would have big task to restore ailing party's fortunes
* Hopes to imitate father Pierre's magnetism
(Adds quote, background on cross-Canada tour)
By Rita Devlin Marier
MONTREAL, Oct 2 (Reuters) - The charismatic son of former Canadian Prime Minister Pierre Trudeau declared his candidacy for the leadership of the Liberal Party on Tuesday, hoping to recreate the sort of buzz that made his father prime minister in 1968.
Justin Trudeau said he was entering the race to lead Canada's oldest political party t o serve his country.
"I love this country, I want to spend my life serving it. This is why tonight I am offering myself for the leadership of the Liberal Party of Canada," Trudeau told a packed hall in Montreal for the well-publicized announcement.
Because of his name and an army of more than 150,000 Twitter followers, Trudeau has become the immediate front-runner in the race to head a party that has become a pale shadow of itself, reduced last year to third place in Parliament for the first time in its 145-year history.
Trudeau, 40, has a youthful magnetism that he hopes to leverage into a reprise of "Trudeaumania," the wave of popularity that engulfed Pierre Trudeau in the go-go years of the 1960s.
In his speech, Trudeau signaled that like his father, he was for a united Canada and a foe of separatist forces that have long dogged politics in his home province of Quebec. The separatist Parti Quebecois was returned to power in a narrow victory in September.
"I also want to build a country ... worthy of my dreams. But for me it goes from the Atlantic to the Pacific, from the Great Lakes to the great North," he said to the cheering throng.
Trudeau, a former school teacher who is married with two children, is embarking on a cross-Canada tour to drum up support for his leadership bid, beginning in Calgary, Alberta, where the Liberal party has little voter support.
An inevitable question pundits raise is whether Trudeau, who has registered few accomplishments in his four years in parliament, will be able to convince Canadians in the 2015 election he has the substance needed to be prime minister.
In the run-up to Tuesday's announcement, he highlighted just
four, relatively minor policies on the issues section of his website justin.ca.
His critics will say he is running on his name, which carries the same dynastic weight in Canada as Kennedy or Bush in the United States.
He will also be vulnerable to attacks for having speculated in February about backing Quebec separatism if Canada moved too far to the right , a surprising view given his late father's staunch opposition to Quebec independence.
His Liberal Party has been squeezed on the left by the New Democratic Party, which replaced it in 2011 as the official opposition, and on the right by the Conservative Party of Prime Minister Stephen Harper.
The Liberals governed Canada for nearly 69 years in the 20th century, but were reduced to only 19 percent of the popular vote in last year's election.
An online poll taken last week as news emerged of his impending candidacy saw a Liberal Party under Trudeau leaping to the lead with 39 percent support. The same poll showed that without Trudeau, the Conservatives would be back in first place, the NDP in second and the Liberals in third.
Analysts caution that until his policies become better known, such a survey was not a reliable predictor of an election result. It does, however, give some indication of Trudeau's potential impact.
(Writing by Randall Palmer in Ottawa; Editing by Russ Blinch and Eric Walsh)
Keywords: CANADA POLITICS/TRUDEAU