Washington ? Millions of low-income senior citizens, disabled veterans and others have not filed to receive the economic stimulus checks sent to millions of U.S. taxpayers this spring, pushing federal and state authorities to redouble their efforts to inform more people that they are eligible.

Some of those people, who do not file tax returns, apparently were not aware that they were eligible for the money or did not file to get the payment.

Under the $170 billion stimulus package Congress approved to boost the economy, most taxpayers are eligible for rebates of as much as $600 ($1,200 for married couples). Parents also receive $300 for each child younger than 17.

Some people who do not file tax returns, including low-income seniors, disabled veterans, disabled people receiving Social Security and some retired railroad workers, are also eligible for the rebates, but they must go through a special filing process to receive them.

Internal Revenue Service (IRS) officials identified about 20 million such people nationwide this year and sent them letters explaining their eligibility, along with a tax form and instructions. But 5.2 million of those eligible have not claimed more than $1.6 billion in benefits, according to the center’s analysis. The IRS sent out another round of eligibility letters last week.

As of July 11, 112 million payments totaling $92 billion had been made to taxpayers nationwide, federal officials said.

As energy, food and health-care costs continue to rise, the rebates can provide struggling families some relief, advocates and federal officials said.

“For people on a fixed income, this is money that can help,” said Nancy Mathis, an IRS spokeswoman.

She said the difficulty has been in reaching people who did not receive or did not respond to the first mailing. The IRS is working with several organizations, including AARP and the United Way, to develop online and community outreach efforts. Advocacy groups have been visiting retirement communities and nursing homes to seek those who have been hard to find.