WASHINGTON  The government watchdog overseeing the federal stimulus program testified Thursday that he could not vouch for the Obama administration’s recent claims that the money had saved or created 640,000 jobs. He suggested that the administration should have treated the number with more skepticism.

The 640,000 figure, announced by the White House with some fanfare last month, came from reports filed by recipients of the stimulus money, many of which have been shown to be inaccurate or overstated since they were made public. But the watchdog, Earl E. Devaney, the chairman of the Recovery Accountability and Transparency Board, said that it was also possible that the figure understated how many jobs were affected. Up to 10 percent of the recipients had not filed the required reports showing how many jobs they had created or saved, he said.

“I have no doubt that there’s a lot of jobs being created,” Mr. Devaney said at a hearing of the House Oversight and Government Reform Committee. “I think it could be above or below 640. I think missing reports might drive the job numbers up, and I think there’s enough inaccuracies in here to question if the 640 number might go down.”

When the White House announced the figures three weeks ago, officials hoped to reassure people that the $787 billion stimulus program was working in the face of rising unemployment. Many economists credit the stimulus with helping the economy, but tallying the actual jobs has proved difficult. A series of embarrassing reports  of raises being counted as new jobs, of jobs claimed in Congressional districts that do not exist, of school districts claiming to have saved the jobs of more teachers than they employ  may have ended up undermining confidence in the stimulus program.