Washington ­- Barack Obama’s supporters are giving him more than just record amounts of cash. They also are providing personal information that may make his donor list the most powerful tool in American politics.

Even if the Democratic presidential candidate doesn’t succeed in his White House bid, this data will make Mr. Obama a power broker in the party for years to come. For the interest groups or Democratic candidates he chooses to sell it to, it would provide a gold mine of information and access to potential donors.

Almost 2 million people have entered personal information on Mr. Obama pages on social-networking Web sites such as Facebook, MySpace, and his campaign’s mybarackobama.com, offering home addresses, phone numbers, their views on specific issues, and the names of friends. The data have allowed Mr. Obama, 46, to raise more than $200 million, fill sports arenas with supporters across the nation and motivate millions more with custom-tailored messages.

“It’s gigantic,” the chief executive officer of Catalist, a company that maintains a database of 280 million Americans, Laura Quinn, said. The list is as “transformational” as the advent of political advertising, she said.

The Illinois senator’s biggest innovation is in persuading people to enter personal information directly on his campaign’s Web site, according to the executive vice president of Grassroots Enterprise Inc., a Washington-based Internet marketing firm that advises campaigns, Bill McIntyre.

Mr. McIntyre, a Republican and former chief national spokesman for the National Rifle Association, said the data entered by 800,000 names on mybarakobama.com may be worth as much as $200 million. While in the past, campaigns have cross-referenced lists of registered voters against other records such as credit-card purchases or magazine subscriptions to find potential supporters, Mr. Obama’s information is more accurate because it relies on data that donors provide themselves.

“When people give information online, they are going to be more truthful and more credible because they are in the privacy of their own environment,” Mr. McIntyre said.

It’s the kind of detailed information that Republican operatives such as Karl Rove, who directed President Bush’s campaigns, excelled at gathering through expensive microtargeting techniques that combine data from several sources. The Democrats responded with Catalist, a similar list-building effort organized by top Clinton campaign adviser Harold Ickes that sells its data to “progressive” causes and candidates, according to its Web site.

Mr. Obama’s success stems from a decision early in his campaign to embrace the concept of social networking, allowing him to leap ahead of his Democratic rival, Senator Clinton, or the presumptive Republican nominee, Senator McCain.