BOSTON – John Kerry will leave here as his party’s presidential nominee after promising a polarized national electorate Thursday night he can make the country stronger at home and more respected in the world.

“We can do better and we will,” the Massachusetts senator said in his much anticipated acceptance speech to the Democratic National Convention, where delegates the day before overwhelmingly nominated him to challenge President George W. Bush in November.

“For us, this is a country of the future,” he said.

Much of Kerry’s 50-minute address to the bursting FleetCenter crowd was devoted to national security. Kerry, a decorated Vietnam War veteran, sought to assure voters it is safe to replace Bush despite the continuing war on terrorism and increasing casualties in Iraq.

“I defended this country as a young man, and I will defend it as president. Let there be no mistake: I will never hesitate to use force when it is required,” Kerry told the tens of thousands of sign-waving Democrats who welcomed this city’s favorite son home with rousing applause, even drowning Kerry out at times during the speech.

Kerry’s talk was more personal in nature than many during the preconvention campaign, throughout much of which he maintained an edge over Bush in national polls.

While such polls can effectively gauge the popular vote at any given time, political pundits say a candidate’s performance in so-called battleground states become true tests of a campaign’s mettle in a close race, as is expected in November.

Richard Powell, a University of Maine political scientist, said Thursday that the national electorate is so polarized, he didn’t anticipate a significant jump in the polls for Kerry, despite the constant media coverage and positive message coming out of the national convention.

“Attitudes are so hardened,” Powell said, attributing the trend, in part, to the stark differences between the two presidential candidates. “People are becoming more committed to their candidates, and earlier.”

But with Bush’s percentage of support stuck in the mid-40s and undecided voters apt to vote for the challenger, Powell said it could be “a difficult road for Bush” in coming months.

Maine is considered one of 17 battleground states. While some studies consider the state’s southern congressional district still a safe bet for Democrats, Maine’s northern district has remained a tossup because of its independent voting history and the slim margin by which Bush lost there in 2000.

Maine delegate Leslie Harlow’s hometown of Sullivan lies within that hotly contested district, where Bush lost by less than 2 percent of more than 300,000 votes cast.

In her tiny Hancock County town, Bush bested Democrat Al Gore by just 28 votes. Harlow said she was certain her training at the national convention – her first – would help her turn those numbers around.

“This is really significant,” Harlow said, adding she would focus on gaining the women’s vote in her area and begin that focus after Labor Day, the traditional start to the no-holds barred campaign. “I know I can have an impact.”

The Bush campaign, however, has already set down roots in northern Maine, setting up its state headquarters in Bangor several months ago and concentrating its grassroots campaign in the region.

Both campaigns have high profile visits scheduled next month, and both candidates are expected to visit the state at least once before the election.

Peter Cianchette, Bush’s campaign chairman in Maine, said he was confident the organization could effectively convince voters that Kerry didn’t share their values.

“John Kerry is not a candidate of conviction,” Cianchette said, repeating the campaign’s almost daily accusation that Kerry “flip-flops” on issues. “These are difficult times, and no time to lead based on political expedience.”

While Kerry is sure to leave Boston on a high after this week’s convention, August could prove a rough spot in the Massachusetts junior senator’s bid to wrest the White House from the Republican incumbent from Texas.

Kerry, in accepting his party’s nod Thursday, triggered a spending limit of sorts, with the Federal Election Commission set to forward a $75 million check to his campaign. Kerry can use only that public money through Election Day on Nov. 2.

Because Bush officially will not accept his party’s nomination until early September, he can still continue to raise and spend private money – much of which will go to television advertising. He can then reserve his public funds for the campaign’s final two – instead of three – months.

In May, the Kerry camp floated the idea of delaying the nomination one month in order to stay on equal footing with the Bush campaign. Unpopular with the party, the idea quickly fell by the wayside.

Kerry’s Thursday acceptance of the nomination, along with vice-presidential nominee John Edwards’ upbeat Wednesday address, did serve to inspire the Democratic faithful in Boston – including Harlow.

But, she said, the convention’s long days and late nights might put any heavy-duty campaigning on hold – at least for the weekend.

“I’m going to spend Saturday sitting around my swimming pool,” a weary Harlow said while on the convention floor before Kerry’s speech. “I am so burned out.”

On the Web: www.johnkerry.com; www.georgewbush.com; www.democrats.org.