ST. LOUIS, Missouri (AFP) - With the 2008 presidential election boiling down to a handful of battleground states, the tightest race of all has emerged in Missouri, the most accurate political bellwether state in US history.

The campaigns of Barack Obama and John McCain are taking a no-holds-barred approach to the midwestern "Show Me" state, and with good reason; Missourians have voted for the presidential winner in all but one election since 1904.

With such imposing history dictating outsized attention for the state, Republican McCain made two stops in Missouri in late September while Democrat Obama earlier launched a bus tour of the state's Republican stronghold southwest.

Officials from both parties concede the campaigns are pouring resources into the state in a mad dash for Missouri's 11 electoral votes.

The candidates have blitzed the state with political ads, with Obama reportedly spending six million dollars on media advertising and McCain close on his heels with 5.5 million.

Missouri's vote is on a knife edge, and recent major polls have toggled back and forth; Thursday's average of recent polls by independent website shows McCain at 47.8 percent and Obama at 47.4 in Missouri. The previous day it was Obama 47.8, McCain 47.5.

"Missouri is in the middle of the country geographically but also the center of the country politically," Washington University history professor Peter Kastor said.

"It is a state where various regional political cultures all exist."

That could favor Obama, Kastor said, as he has the passionate oratory skills of the deep South combined with a hard-driven persona of a cosmopolitan Northeasterner.

But he will have to overcome latent racism among rural whites, an element more than one expert described as an "unknown quantity" in Missouri particularly because residents have seen so few black candidates run for state or national office.

The state looms especially large for the Republicans, both parties agree, as they trail in most of the other swing states including Florida, Ohio and Virginia.

"Senator McCain has to win Missouri to win the White House. So there is a strong commitment from the McCain-Palin campaign to make sure that we deliver Missouri for that ticket," said Jared Craighead, executive director of the state's Republican Party.

Earlier this month McCain pulled resources out of Michigan, essentially conceding it to Obama. Officials in both parties expect those resources to be shifted to Missouri.

The Obama campaign has opened 40 field offices across the state, with more than 100 paid staffers -- "an unprecedented commitment to Missouri," said Jack Cardetti, communications director of the Missouri Democratic Party.