By NANCY BENAC

WASHINGTON _ Kriss Riggs isn't one to spend her money on politicians.

"Even the place you can donate a dollar on your taxes, I refuse to do it," says the 60-year-old photographer from Blue River, Ore.

Likewise for Kate Schwartz, a 24-year-old marketing expert from Chicago. Past elections, she says, always seemed far removed from young people.

"A lot of people felt like it wasn't happening in my demographic," Schwartz said.

Not this time.

Riggs and Schwartz are foot soldiers in Barack Obama's 1.5-million-strong army of campaign contributors. Dozens of Associated Press interviews with donors, and an AP financial analysis show how contributions that make only a soft ca-ching by themselves, arriving in increments of $10, $15 and $50, have collectively swelled into a financial roar that has helped propel Obama toward the Democratic president nomination.

Altogether, Obama's campaign has taken in an unprecedented $226 million, most of it contributed online. His donor base is larger than the one the Democratic National Committee had for the 2000 election.

These are hardly political fat cats. Ninety percent of his donors give $100 or less, and 41 percent have given $25 or less, according to the Obama campaign. Overall, he has raised 45 percent of his money in small contributions. Hillary Rodham Clinton's figure is 30 percent, Republican John McCain's is 23 percent.

Riggs and Schwartz are examples of how Obama has become a financial colossus: Neither had given money to a candidate before; both have donated to him more than once; both expect to continue giving. And, just as significantly, they've gone on to help the campaign in other ways, staffing phone banks and canvassing neighborhoods.

In interviews with small donors around the country, the same message comes through: These donors feel they've taken ownership. They believe they're helping to set Obama free from the tug of big-money corporations and special interests.

Says Aaron Alpern, a 46-year-old actor from Chicago: Donors like him "don't have the pull of a gigantic corporation, but we have sort of the reverse — we give him freedom."

An AP analysis helps to fill in the portrait of Obama's small donors.

They are more broadly dispersed than Clinton's. People whose small contributions to Obama add up to at least $200 can be found in more than 14,000 ZIP codes nationwide, compared with a little less than 12,000 for Clinton, and less than 9,000 for McCain. Conversely, the 10 ZIP codes that contributed the most to Clinton's campaign account for more than 15 percent of her total contributions, while Obama's top 10 ZIP codes account for less than 5 percent of his take. McCain's top 10 ZIP codes account for just over 11 percent of his total.

Obama, a magnet for younger voters, is cashing in on that phenomenon. Among small donors, students have given $303,000 to him, compared with less than $100,000 to Clinton and less than $20,000 to McCain.