The Democratic and Republican parties are struggling to engage new voters in this year's presidential race, with an apparent deficit of enthusiasm suppressing the number of people who have registered to vote ahead of the 6 November election.

A Guardian survey of six of the most crucial swing states upon which the outcome of the presidential ballot is likely to depend has found that new voter registrations recorded between January and August this year are markedly down compared with the same period in 2008. The drop is particularly pronounced in several states for the Democrats – a likely indication that Barack Obama's re-election team has been unable to match the exceptional levels of voter excitement generated by his candidacy four years ago.

The six states included in the Guardian survey – Colorado, Iowa, Florida, Nevada, Ohio and Virginia – are all being bitterly fought over by Obama and his challenger Mitt Romney. Backed by their respective Democratic and Republican parties, both candidates have sought to maximise turnout by running registration drives in an attempt to attract new voters to their cause.

The Republicans this year have also pursued an aggressive policy of challenging voter rolls in an attempt to wheedle out what they claim are fraudulent names. The Democratic party and voter rights organisationshave accused the Republicans of acting maliciously in an attempt to suppress the number of black, poor, elderly and young people registering to vote.

The biggest decline among registered voters within the surveyed swing states was in Florida. Between January and July this year, the state added 224,750 voters – 82,638 fewer than the same period in 2008. A similar comparison of the first seven months of 2012 and 2008 shows a dip in voter registrations of 25,486 in Iowa, 23,009 in Virginia, 19,199 in Nevada and 9,566 in Colorado.

The declines look particularly dramatic on the Democratic side, largely as a reflection of how well the Obama campaign did in mobilising new voters in its first run on the presidency in 2008. This year it has clearly struggled to repeat the performance.

In Iowa, Democrats registered 69,301 voters between January and August 2008, but over the same period this year the party's voter roll dropped by more than 45,000 as a result of the voting rolls being purged. Republicans in Iowa by contrast held relatively steady – they put on 7,515 voters in the first eight months of 2008 and 5,671 this year.

If previous elections are any indication, however, swing states will see a bump in voter registrations in the final two months before the election. In 2008, Iowa registered 3,232 more Democratic voters in September and 7,076 in October. A spike was also felt in Nevada, where Democrats registered 32,729 voters in September and 26,550 voters in October.

In 2008, Obama's Florida registration efforts played a crucial role in securing him the state, and with it the presidency. That year, the Democrats registered a thumping 196,490 voters while Republicans signed up just 54,394.

Yet in 2012, Democrats have only mustered about a quarter of their huge successes last time round: 50,909 voters. Republicans have also held steady in this state with 56,154 new registrants this year compared to 54,394 in 2008.

Voting rights experts in Florida blame the overall slump in registrations this year – with 82,638 fewer voters being registered between January and July than in the same period in 2008 – on a spate of aggressive legislation coming out of the Republican-controlled state assembly. The laws, which included threats of criminal prosecution for volunteers should they not follow the rules by the letter, had such a chilling effect that many non-partisan organisations suspended their voter registration operations entirely.

The League of Women Voters of Florida stopped registration drives for more than a year, until the courts intervened and overturned the new laws on the grounds that they were unconstitutional. The league's president, Deirdre Macnab, said that the Guardian's figures confirmed the pernicious impact of voter suppression laws in the state.

"The voter suppression laws have served to inhibit and repress crucial voices that need to be heard in our elections. They were playing politics with our voting rights," she said.

Macnab added that the suspension of voter registration drives had a particularly adverse impact on communities that traditionally suffer from low election turnout such as poor people, ethnic minority voters, students, older and disabled people. All those groups tend to lean towards the Democratic party, helping to explain the fact that registration is sharply down for Democratic voters this year while Republican figures have remained stable.

In Ohio, voter rights activists are reporting low levels of political enthusiasm. This classically politically divided state, which Obama won in 2008 with just 51.5% of the vote, is showing a clear drop in the number of new registered voters.

The manner in which Ohio tabulates its data makes it difficult to compare with other states. Whereas most states compile an aggregate of registered voters, Ohio only counts how many new voters register every month. That said, the trend stands when comparing new registration numbers month to month. In July and August 2008 Ohio registered 76,227 and 81,479 voters respectively. In 2012 during the same months voter rolls were 51,964 and 78,681.

Sean Sukys, a volunteer with Rock The Vote in Ohio, which encourages young people to participate in the democratic process, said he had been taken aback by how many people said they didn't care about the election this year. "It's surprising to me that they'd say they didn't care about the future of the country – but then America is not the most educated population so maybe it's only to be expected."

While the decrease in registrations may have something to do with the tone of the election itself, the Lawyers' Committee's manager for legal mobilization Eric Marshall cited voting restrictions as an undeniable contributor. "Our voter registration system is stuck in the 19th century. Unfortunately, the discourse in our democracy right now is more focused on policies that make it hard for certain people to vote," he said.

© 2012 Guardian News