To date, the IRS has issued nearly 30 million stimulus checks, totaling more than $27 billion. The rebates range from $300 to $600 a person, or $1,200 for a married couple. Parents with dependent children are eligible for an additional $300 per child.

This is the first time the IRS has used direct deposit to deliver rebates a step intended to quickly pump money into the struggling economy. But several problems have delayed the process:

Taxpayers who applied for refund-anticipation loans or who had their e-filing fees deducted from their refunds won't receive their rebates by direct deposit, even if their regular tax refunds were delivered that way. Through April 17, more than 20 million taxpayers applied for such loans or had fees deducted from their refunds, according to IRS data.

Those taxpayers will have to wait for their checks to arrive by mail. The IRS is scheduled to mail rebate checks May 16 through July 11, based on taxpayers' Social Security numbers.

Allan Hurlock, 40, a systems engineer in Springfield, Pa., says he thought he would receive his rebate on May 9, based on the IRS schedule for direct deposit and his Social Security number. After numerous calls to the IRS, he finally reached someone who explained that his check would arrive by mail because the fees he paid TurboTax to e-file his tax return were deducted from his refund.

Taxpayers whose fees were deducted or who took out refund-anticipation loans are receiving paper checks because those loans involve a third-party bank account, the IRS says.

About 350,000 eligible households that have received rebates didn't receive the additional $300 payment for their children. In some cases, the extra payments were withheld because people failed to check a box on their tax return indicating to the IRS that their children were eligible, IRS spokesman Terry Lemons says. In other cases, the error occurred because a few tax software companies failed to provide the information the IRS needed to make the payments, Lemons says. The IRS plans to mail a "catch-up payment" to the parents by July.

Taxpayers who filed jointly with a spouse who doesn't have a Social Security number won't receive a rebate at all. They include thousands of legal residents whose spouses have applied for a Social Security number but haven't received one yet.

Faced with a deluge of phone calls, the IRS is urging taxpayers to go to its website, www.irs.gov, for more information. "We encourage people to be as patient as they can," Lemons says. "Calling on the phone won't help people get their payments any quicker."