A torrent of secret money is flooding into the leading presidential campaigns, with more than $118 million, or one-quarter of the total raised in this cycle, banked without disclosure of who gave the funds or where the donations originated.

The money is coming from hundreds of thousands of donations of $200 or less, which have been widely praised for democratizing the system for funding White House bids. However, the surge in low-dollar gifts has come at the cost of transparency, since federal law only requires campaigns to itemize donations when a donor gives more than $200.

According to an analysis being released today by a Washington think tank, the Campaign Finance Institute, Senator Obama of Illinois led the pack with such small and secret donations, pulling in about $31 million during 2007. Rep. Ron Paul ran second in small gifts, raking in more than $17 million. At the end of the year, Senator Clinton and John Edwards, who has since dropped out, were essentially tied for third in unitemized, small contributions, with each candidate raising about $11 million.

Advocates of tighter campaign finance controls said the notion behind excusing donations of under $200 from the reporting requirements was that the sums were insignificant from an ethical perspective. “The idea is, it is too small an amount to worry about in terms of you’re not going to buy significant influence or access for $200,” a spokeswoman for Common Cause, Mary Boyle, said.

However, one area of concern with the flood of donations, particularly those made online, is that foreigners could be weighing in illegally in an American election. Mr. Obama’s Web site allows donors to choose an address in one of 227 possible countries or territories, including Iran, Iraq, Zimbabwe, and Yemen.

Mr. Paul’s site is even more embracing, permitting addresses in Syria and the “Occupied Palestinian Territories.” Michael Huckabee’s Web site seems to require an American address to make a gift. Donors to Senator McCain need to put in a ZIP code of some sort, but not a state.

While it is a crime for most foreigners to donate to American campaigns at the federal level, those with so-called green card status can donate legally, as can Americans who live abroad.

The most cautious campaign when it comes to accepting online donations from overseas seems to be that of Mrs. Clinton. Visitors to her Web site who want to list an address abroad are directed to a special page which advises that such donations are only taken by mail and that donors “must include a copy of your U.S. passport or green card.”

“The mail-in requirement provides an additional level of review that would not occur with an online contribution that is automatically processed,” a spokesman for Mrs. Clinton, Blake Zeff, said.

Spokesmen for Mr. Obama and Mr. McCain did not respond to inquiries about their screening system for gifts coming from abroad. The donation pages for all the candidates remind donors that they must be American citizens or legal residents. Mr. Paul’s site also has a pop-up feature which asks any donor with a foreign address to confirm American citizenship.

However, an aide to Mrs. Clinton suggested that these mechanisms do not go far enough. “A foreign national could misrepresent his or her citizenship when contributing online, by checking the box…when such a representation is not true,” the aide, who asked not to be named, said.

The former first lady’s caution in the area is understandable since during and after President Clinton’s re-election bid in 1996 the Democratic National Committee was forced to return more than $3 million, including tens of thousands of dollars federal investigators traced to China.

Since the law requires that campaigns disclose a donor’s identity when his or her gifts total $200 or more, some small donors are eventually disclosed as their giving is cumulated. However, it is not always easy for campaigns or their computers to figure out whether a series of gifts came from the same person.

“It’s very tricky,” a spokesman for the Federal Election Commission, Robert Biersack, said. “There’s nothing that says you can’t make donations from several different addresses as long as they are legitimate.” While the commission can audit all of a campaign’s donations to ensure compliance with the law, it would usually do so only after receiving a complaint alleging wrongdoing, Mr. Biersack said.

Mr. Paul’s online fundraising is arguably more transparent than that of other campaigns, since he sometimes posts the names of recent donors on his Web page. However, each donor can opt out of that publicity and there is no comprehensive list of gifts.

When the Federal Election Campaign Act was passed in 1971, Congress set $100 as the threshold for public disclosure of political donations. It was raised to $200 in 1979 and has remained there since, despite proposals to raise it further.

In 1999, while George W. Bush was preparing for his first White House bid, he indicated he favored instant disclosure on the Internet of all donations to federal campaigns. A version of that proposal was included in campaign finance reform principles President Bush sent to Congress in 2001. Congress passed an overhaul of campaign finance laws the following year and Mr. Bush signed it. However, the instant disclosure proposal was not included.