WASHINGTON (AFP) - Four days before the presidential election, campaign chiefs for rivals Barack Obama and John McCain are firing up the most intense and targeted voter turnout operation in US history. Next Tuesday, Democrat Obama and Republican McCain will rest their White House aspirations in the hands of campaign foot soldiers in swing states like Ohio, Pennsylvania, Nevada, Florida and Virginia. In a close election, a few thousand votes can make a difference in a battleground state " and the campaigns are already hard at work trying to boost turnout in early voting states across the United States. Both political parties scan voter data in minute detail, studying people's political preferences, key issues, and where they live to fashion tailored political messages in a practice known as "micro-targeting." Democrats hope this year's surge in registered voters backing their party, Obama's huge fundraising edge and sheer enthusiasm whipped up by his campaign " especially among young voters and African Americans " will be decisive. Republicans are relying on their famed 72-hour turnout operation which helped President George W. Bush narrowly capture two terms in the White House. Some political experts believe Obama may have assembled the most sophisticated "ground game" ever seen in US politics " which is already at work driving up Democratic turnout in early voting states. The scale of the Illinois Democrat's machine suggests campaign chiefs may have sketched an intricate, precinct-by-precinct map of exactly who their voters will be on election day. Obama mustered around 1.5 million volunteers in 770 offices spread across the United States and has 1,400 neighbourhood teams in battleground Ohio alone. Campaign workers have been cracking along at a rate of 400,000 voter contacts per day " defined as conversations in person at someone's front door or by telephone. "We have spent a lot of time building our organizational strength, spending the summer building capacity, and really focusing on our voter contact and our neighbourhood organizations," said Obama's national battleground state chief Jennifer O'Malley. "We really feel that, in a number of these states ... this election is going to come down to our ground organization and what happens in the final days of the campaign." It is that direct contact between Obama canvassers and undecided voters that could be crucial, said Joshua Dyck, a political scientist at the University at Buffalo. "That face-to-face contact in your neighbourhood is the kind of thing that gets through to people," he said. Obama teams refined the technique in Iowa, where local canvassers proved more effective than outsiders from out of state before his primary triumph. The Illinois senator was helped by the long, bitter Democratic primary against Hillary Clinton, which forced him to build a deep nationwide operation. A former community organizer, Obama may also have instinctively understood how to build a block-by-block support base " in fact he had to beat the Clinton political machine. Republicans will roll out a "72-hour strategy" this weekend, with tens of thousands of phone calls and voter contact visits to motivate their voters. "This sort of vaunted 72-hour plan has been very successful in the last two cycles, the (Republicans) can still put something together, especially in Florida and Ohio," said Dyck. Political guru Karl Rove's famed micro-targeted operation helped Bush to two slim victories in 2000 and 2004. In 2004, Democrats believed even deep into election night that their huge increase in turnout in the key swing state of Ohio would be decisive. But Rove masterminded a below the radar showing among rural "values voters" earning himself the nickname the "architect" from his grateful boss. McCain's campaign said Friday that it had made 5.3 million targeted phone calls and door knocks in the last seven days and 1.3 million on Thursday alone. But still some Republicans look at the Obama machine and worry. "He has had an amazing organization down to the street level, I've never seen anything like it," former Republican presidential candidate Mike Huckabee said on CBS on Friday. "It's stunning, it's impressive and he has done something I've never seen in any candidate. "George Bush in '04 had a massive 72-hour effort, but it pales in comparison to the detail of Barack Obama's ground game."