WASHINGTON – Democratic presidential hopeful Sen. Barack Obama, D-Ill., who has decried Wall Street profits and CEO pay, has tapped a vein of donors among bankers and financiers who have given generously and helped drive his successful presidential campaign sprint for cash.

Among the firms whose employees gave the most to Obama in the second quarter of the year were Lehman Brothers, Goldman Sachs, Citigroup and JP Morgan. Their money, much of it the maximum donation allowed by law, placed Obama in competition with Sen. Hillary Rodham Clinton for high-finance dollars in her own backyard of New York.

For Obama, the money represents one side of a fundraising and support-building equation. The other is the campaign’s outreach to small donors – a concerted effort to build a broad network of contributors who give less than $200.

The campaign has built that network aggressively, charging $25 a person to attend rallies and even counting buyers of Obama T-shirts and bumper stickers as donors.

In all, Obama came out of the first six months of the year as the top fundraiser among all candidates and is sitting atop the largest amount of cash on hand in either the Republican or Democratic fields.

“It’s really astounding to me that this underdog candidate is way out ahead in fundraising,” said Michael Malbin, executive director of the nonpartisan Campaign Finance Institute. “He’s running neck-and-neck with everybody else in large contributions. His advantage is in the small contributions.”

Obama, marching with workers striking at a hotel in Chicago, said his financial success is a function of momentum.

“The fundraising is an expression of the enthusiasm at the grass-roots levels,” he said.

So far this year, Obama has collected $16.4 million in donations under $200 – that is 29 percent of his total primary election contributions of $56.8 million. The small donations have come in through the Internet, in the mail and from those attending about a dozen rallies in cities across the country.

Attendees count toward the 250,000 donors that the campaign says it has amassed this year. So do online purchasers of merchandise who pay $20.08 for an Obama T-shirt or $2.50 for a campaign placard. Campaign spokesman Bill Burton said such small donors account for “less of half of 1 percent of all donors.”

“A lot of those folks have given otherwise,” Burton said. “It’s probably even a smaller number than that.”

The challenge for Obama now is to turn those donors into a volunteer force that will make a difference in early presidential nomination contests, especially Iowa, New Hampshire and South Carolina.