WASHINGTON — The 2012 presidential campaign was expected Thursday to pass the $2 billion mark in fundraising, according to accounting statements submitted to the government, thanks to an outpouring of cash from ordinary citizens and the wealthiest Americans hoping to influence the selection of the country’s next leader.

The eye-popping figure puts this election on track to be the costliest in history, fueled by a campaign finance system vastly altered by the proliferation of “super” political committees that are bankrolling a barrage of TV ads in battleground states.

President Barack Obama and Republican challenger Mitt Romney had brought in more than $1.5 billion through the end of September, according to previous fundraising reports submitted before the final pre-election accounting statements were due Thursday night.

Obama hadn’t yet disclosed his fundraising for early October, but Romney’s campaign said it raised $111.8 million in the first two weeks. Added to that was more than $230 million in donations involving super PACs since 2011.

The largest of those were two pro-Romney groups. American Crossroads, a Republican-leaning super PAC with ties to former President George W. Bush’s longtime political counselor Karl Rove, reported raising at least $68 million through September.

Restore Our Future, founded by former Romney aides, reported raising $110 million so far. Priorities USA, a pro-Obama group founded by two former aides to the president, reported raising $50 million through last month.

The $2 billion fundraising figure doesn’t include nearly $130 million spent on political ads by non-profit groups that aren’t required to file campaign finance reports or disclose their donors.

Such so-called social welfare organizations are governed by tax laws, not election laws, although they are often affiliated with established super PACs.

Presidential candidates in 2008 raised more than $1.8 billion in inflation-adjusted figures. This time, new factors have contributed to the sharp escalation in the campaign money chase.

This year marked the first time that both major party candidates opted out from the public financing system established to set limits on how much a presidential candidate can raise and spend. Obama and Romney would have been eligible for about $100 million in taxpayer money to support their campaigns through the general election, but both gambled, correctly, that they could raise and spend far more.

In 2008 Obama became the first presidential contender to refuse all public financing while his Republican rival, Arizona Sen. John McCain, accepted the government funds.

The lopsided result — Obama outspent McCain by more than 2-to-1 in the general election — effectively ended public funding as an option for serious candidates.

With the 2012 election so tight, Obama and Romney have spent considerable time at high-dollar fundraising events courting wealthy donors. Romney last month lamented the time spent fundraising rather than speaking to larger groups of voters.