WASHINGTON — Uncle Sam is in your debt — to the tune of more than $16 trillion and counting. But Americans have been voluntarily contributing to help pay the government's IOU, donating more than $7 million in the just-completed fiscal year.

Lawmakers want to make it even easier for patriotic folks to contribute. The House recently approved and sent to the Senate legislation that would establish a check-off box on income-tax returns for donations to pay down the debt.

The Bureau of Public Debt received $7,694,091.70 in voluntary contributions from the beginning of October of last year through the end of August this year, including about $1.9 million from one estate, according to the latest figures.

Contributions for September, the final month of the 2012 fiscal year, have yet to be reported. But the contributions were more than double the nearly $3.3 million donated the previous fiscal year and represent more than any annual amount since $20.7 million in contributions in 1994.

The Bureau of Public Debt does not disclose donors' names.

The Los Angeles Times last fall spotlighted the little-known donations program in a profile of a retired Texas postal worker who donates a portion of his pension, plus whatever he makes from collecting aluminum cans in his neighborhood, for debt reduction.

Atanacio Garcia has contributed $2,997.88, his son said.

The donations program has been around since the Kennedy administration, and the Bureau of Public Debt has made it easier to receive donations by accepting credit and debit cards online. But some lawmakers say the program isn't widely known and, therefore, proposed the check-off box on tax returns.

Republicans named the legislation to create the check-off box the Buffett Rule Act in response to President Obama's call for raising tax rates on income beyond $250,000 a year for couples.

They noted the president has cited billionaire investor Warren Buffett's complaint he pays a lower tax rate than does his secretary. The bill's sponsors say it would allow proponents of higher taxes to "put your money where your mouth is" and voluntarily send more money to Uncle Sam.

Pete Sepp of the National Taxpayers Union suggested taxpayers be allowed to check off up to 10 percent of their tax liability, with a cap of perhaps $1,000 per return — and a requirement the money go for debt reduction.