Forget the ads, debates and endorsements.

Come Tuesday, the only thing that matters for the candidates vying for the late Edward Kennedy's Senate seat is getting more of their voters to the polls than anyone else.

A strong field operation, key in any major campaign, is all the more critical given the odd timing of the Massachusetts primary in early December and the fact that there are no other races on the ballot.

"This is a very unusual situation," said Secretary of State William Galvin, who predicted voter turnout could be as low as 300,000 to 500,000.

"We've never had a statewide special election. And it's in the winter, and now I'm hearing about snow. And it's coming during the holiday season," he said.

Each of the four Democratic candidates _ Attorney General Martha Coakley, U.S. Rep. Michael Capuano, Boston Celtics co-owner Stephen Pagliuca and City Year co-founder Alan Khazei _ are playing to their strengths heading into the campaign's final 48 hours as they try to sew up their party's nomination.

Coakley, hoping to become the first woman elected from Massachusetts to the U.S. Senate, has drawn backing from female lawmakers and activists, from state Senate President Therese Murray to Ms. magazine founder Gloria Steinem to the pro-abortion rights group EMILY's List.

Coakley, leading in most polls, says she's not trying to take advantage of her position as the only female candidate, but a strong showing from female voters could prove critical on Tuesday.

Like the other candidates, Coakley is taking to the road in the final days and ramping up her get-out-the-vote drive.

Coakley spokesman Corey Welford said the campaign has spent months identifying voters and is planning on making thousands of phone calls to remind supporters to head to the polls.

"We're taking no vote for granted," Welford said.

Capuano knows the benefits of a strong field operation.

In 1998, Capuano was a five-term mayor of Somerville when he jumped into an open race for the Congressional district that gave Massachusetts Tip O'Neill and John F. Kennedy. Then-Rep. Joseph P. Kennedy II had decided not to seek re-election.

In a 10-way race that included a couple of millionaire candidates and former Boston Mayor Ray Flynn, Capuano was able to use his base of support in Somerville to capture 24 percent of the primary vote _ enough to win the Democratic nomination, and eventually the seat in Congress.

Capuano, who has portrayed himself as the working class underdog in the race, is hoping to repeat that kind of upset on Tuesday.