Continued from page 1

The Obama administration is counting on taxpayers to help it watch the spending. In signing the bill, Mr. Obama launched, a Web site that will publish projects and dollar amounts when they are spent.

The president also called out governors and mayors by name, telling them he’ll be watching them.

“With a recovery package of this size comes a responsibility to assure every taxpayer that we are being careful with the money they work so hard to earn,” he said.

Republicans challenged Mr. Obama to be as vigilant as his promises.

“The federal bureaucracy is now being asked to absorb hundreds of billions of dollars, and the potential for waste, fraud, abuse and mismanagement is something we must be diligent in preventing and addressing,” said Rep. Darrell Issa of California, the top Republican on the House Committee on Oversight and Government Reform.

The president said he used 10 different pens to sign the bill, essentially writing little more than one letter of his signature per pen. The pens are keepsakes given to key aides and lawmakers involved in writing the bill, and the high number of pens showed just how many people had a hand in delivering Mr. Obama’s first major piece of legislation in his young administration.

The White House said Mr. Obama may not be done spending. Press secretary Robert Gibbs would not rule out another spending bill if the economy continues to founder, though he said there are no specific plans at this point.

“The president is going to do whatever he thinks is necessary to get our economy moving again,” Mr. Gibbs told reporters traveling with Mr. Obama.

• Tom LoBianco contributed to this report.