Voter registration has surged, early-voting sites have been besieged and primary election turnouts shattered records in many states. Beyond the numbers, the election has become a subject of constant conversation in workplaces and at home, candidates have become cultural icons and many viewers have found themselves obsessed with television coverage.

"It's the highest engagement I've ever seen-by far," said Abner Mikva, a former judge and Chicago-area congressman who distributed literature for Harry Truman in 1948. "This is the most excited I've ever seen the electorate. There is a feeling in the air-similar but even more so-to when Jack Kennedy was elected."

The biggest reason may be the candidacy of Barack Obama, a young, charismatic African-American whose Democratic campaign has energized voters who previously had shown little interest in politics. On the Republican side, John McCain's running mate, Sarah Palin, who would be the first woman vice president, has driven excitement among conservatives.

The result is "a reawakening of American electoral politics," said Lawrence Jacobs, a University of Minnesota political scientist who studies polling and the presidency. "Not long ago we were bemoaning the withdrawal and cynicism of American voters. This election is showing a consistently intense electorate. People have been following this at a fever pitch for months and months."

Most commentators, of course, applaud that as good for democracy and government. Tuesday is likely to feature scenes from across the country of excited voters, mobbed polling places and people standing in line for hours. But it also raises the possibility that voting systems could crack under the strain of increased turnout, potentially forcing polling places to stay open hours later than scheduled.

"We expect very long lines," said Mary Boyle, spokeswoman for the watchdog group Common Cause. "In states with early voting, I've heard reports of 4 1/2 -hour lines. And that's for early voting, which is over multiple days. On Election Day, we think the whole system will be tested like never before. People need to be patient-bring a snack, bring a book and be ready to wait. Don't think voting is something you'll be able to do in 15 minutes. You won't."

Experts are forecasting a turnout of about 65 percent of eligible voters, the highest in nearly a half-century, since the election of John F. Kennedy in 1960. Before that, it had not been since 1908 that turnout was so high, prompting some to call the 2008 election a "hundred-year storm."

If voters are still in line when polls are scheduled to close Tuesday night, authorities may keep them open longer, which could mean confusion and delays.

Early voting, which in previous years had been a negligible factor, is this year providing a vivid indicator of what is to come. More than 30 million people already have voted, a hefty percentage of the overall 140 million expected to cast ballots to pick the nation's 44th president. Early voters in such states as Florida, Georgia and North Carolina stood in line for hours.

In some states, that likely has siphoned off enough voters to make Election Day go more smoothly. But in others it's merely a warning of how crowded things will get.

"I think of early voting as the early-warning buoy, and it looks like there is a storm coming," said Paul Gronke, who heads the Early Voting Information Center at Reed College in Portland, Ore.

Other signals point in the same direction. Voters turned out in higher numbers for this year's primaries than for any other primary season except 1972, when the country was agonizing over the Vietnam War. Roughly 10 million new voters have registered since 2004, about 5 million more than might have been expected from ordinary trends.

"In my lifetime, we have never had a climate like this one," said Curtis Gans, director of the Center for the Study of the American Electorate. "In 1932 [during the Great Depression], maybe there was a climate like this one."

Voters appear to feel that the country is facing monumental challenges of the sort that come along only every few decades. The global economic system is in crisis, the U.S. is entangled in frustrating wars in Iraq and Afghanistan, and the threat of terrorism continues to loom. Fuel prices are high, as is the cost of health care, and retirement savings are in jeopardy.

Many scholars cite the 1960s, with their social turbulence and intense civic activity, as the last time the public was so engaged with the political process. 

"The difference, of course, is you had the social movements and street protests in the 1960s you don't have now," Jacobs said. "But the level of rejection of the status quo is phenomenal. Eighty-five percent of the people say we're going in the wrong direction. The public anger is palpable."

Obama seems to have tapped into that. With his unprecedented cash reserves, the Democrat has invested heavily in driving up registration, participation and turnout, even in states that rarely have seen much political activity on the presidential level.

And of course, as potentially the first black president of a country that always has been torn by race, Obama's candidacy has caught the imagination of large numbers of African-Americans and young voters, as well as other citizens. Some, including Obama himself, insist that this election will bring to an end the conservative era that began with Ronald Reagan's election in 1980.

The result of all this is a vote that feels historic to many people, and they want to be part of that history.