President Obama and Mitt Romney are both on pace to raise more than $1 billion with their parties by Election Day, according to financial disclosures filed by the campaigns on Thursday.
From the beginning of 2011 through Oct. 17, Mr. Obama and the Democrats raised about $1.06 billion, and Mr. Romney and the Republicans collected $954 million, including some money for the party's Congressional efforts, setting up 2012 to be the most expensive presidential campaign in history.
But the sources of that money, raised over the course of a deeply polarizing campaign, echo the sharp divisions between the two men and their parties over issues like abortion rights, the role of government in regulating industry and the country's economic future.
Wall Street has invested more heavily in Mr. Romney, a former financier who has pledged to repeal Mr. Obama's new financial regulations, than in any presidential candidate in memory. Employees of financial firms had given more than $18 million dollars to Mr. Romney's campaign through the end of September and tens of millions more to the "super PACs" supporting him.
Insurance companies, doctors and law, accounting and real estate firms are giving less to Mr. Obama and the Democratic National Committee than they did four years ago, according to data from the Center for Responsive Politics.
Yet donors in other industries have stepped in. With Mr. Obama making repeated trips to Silicon Valley and holding round tables with executives there, the technology industry has donated about $14 million to the president and the Democrats, substantially more than in 2008.
Retirees, the biggest single source of money for both sides, have given the Democrats much more than they did four years ago, as have employees of women's groups, retailers and hospitals and nursing homes.
To make up for the loss of business money that flowed to his campaign four years ago, Mr. Obama has also turned to the very smallest donors, building an army of millions of supporters who have given as little as a few dollars each. About 4.2 million people sent donations to Mr. Obama and the D.N.C., his campaign said on Thursday, roughly one million more than in 2008.
Over all, 55 percent of the Obama campaign's money through the end of September came in donations of less than $200, including from many people who have repeatedly sent in small checks over the course of the campaign. Just 13 percent of his checks were for $2,500, the maximum that donors are allowed to contribute for either the primary or general election.
Mr. Romney, by contrast, has cultivated business leaders and benefited from a Republican donor establishment that is eager to defeat Mr. Obama, raising an unprecedented amount of money from wealthy donors who gave the maximum allowed. Just 22 percent of his cash has come from donations of less than $200. Through the end of September, 45 percent of checks to Mr. Romney's campaign were for the maximum $2,500 contribution.
Neither candidate is likely to raise as much money directly for his own presidential committee as Mr. Obama did in 2008. A flood of online donations that year, and support from many traditionally Republican donors, helped Mr. Obama raise $748 million for his presidential committee. The D.N.C. raised another $244 million, bringing the combined total to a little under $1 billion.
This time around, Mr. Obama, as an incumbent, has raised more of his total through the D.N.C., which can accept five-figure checks from each of Mr. Obama's wealthiest supporters. By raising more money from his very biggest and very smallest donors, Mr. Obama has been able to offset his losses from the business world and from previous contributors who gave less or not at all this time, whether because of the recession or fading enthusiasm.
Mr. Romney, after becoming the presumptive Republican nominee in the spring, almost immediately began a fund-raising effort with the Republican National Committee, several state parties and the two Congressional campaign committees. Mr. Romney's total through September included about $13.6 million that was raised for and transferred to the National Republican Senatorial Committee and the National Republican Congressional Committee.
The overall totals do not include hundreds of millions of dollars being raised and spent by "super PACs" and other outside groups, mostly to benefit Mr. Romney and other Republicans. Groups aligned with Mr. Romney have spent $302 million on campaign advertising that they are required to disclose to the F.E.C., compared with about $120 million for groups aligned with Mr. Obama. Tens of millions of dollars more has been spent on issue advertisements whose precise costs are difficult to measure.
"As the Romney campaign and their 'super PAC' allies continue to outspend us on the air, we're making every effort to expand our donor base heading into the final stretch," said Adam Fetcher, an Obama spokesman.
Mr. Romney and the Republicans raised about $21.3 million more than Mr. Obama and the Democrats during the first 17 days of October, according to the disclosures filed on Thursday, as Mr. Romney rose in the polls and performed well in debates, emboldening his supporters.
Mr. Obama and the Democratic National Committee took in $92.4 million during that period, after surpassing Mr. Romney in August and September.
Mr. Romney and the R.N.C. raised $113.7 million over the same period, the final days for which the campaigns are required to report their fund-raising before the election on Nov. 6. Mr. Romney and his party also spent about $146.2 million during the first 17 days in October, slightly less than the $149.7 million spent by Mr. Obama and the Democrats.
While Mr. Obama's team invested tens of millions of dollars early in the campaign to identify, contact and raise money from grass-roots voters, those expenditures have left the Republicans with more cash in the final weeks of the election that could finance a late surge of advertising. Mr. Romney and the G.O.P. ended the final filing period with $169 million in cash on hand, significantly more than the $123.8 million held by Mr. Obama and the Democrats.
Michael Luo and Derek Willis contributed reporting.