Every year people travelling through U.S. airports mistakenly leave behind about $400,000 at security screening sites. Transportation officials now apply the funds to airline security costs.

A bipartisan lawmaker group wants that change to go instead to support USO Inc, a private group that greets U.S. soldiers at airports in addition to sending care packages and entertaining them overseas. But transferring the money to the nonprofit would cost U.S. taxpayers $1 million, a recent government report shows.

The findings from the nonpartisan Congressional Budget Office highlight the accounting judo that can roil the nation's lawmaking process and shows just how complex U.S. budget rules can be at a time of record deficits.

It also underscores tensions with those who think government's hands are already too deep into people's wallets.

To some lawmakers, it should be a no-brainer to simply give away money that doesn't really belong to the goverment anyway.

"One would think that providing a cost estimate for this bill would be straightforward," said U.S. Representative Jeff Miller, who is sponsoring legislation to redirect the money.

"Only in the federal government can change you are forced to remove from your pockets and then accidentally leave behind be counted as guaranteed income to the TSA. This is the problem with our government today," Miller, a Florida Republican, wrote in a newsletter to constituents last week.

At issue is the fact that the Transportation Security Administration has already collected about $1.2 million in forgotten money, according to the CBO. And the TSA, which said it cannot discuss pending legislation, has legal authority to spend it as it pleases for other aviation security measures.

"Requiring the agency to transfer amounts to USO would accelerate outlays," CBO said in its findings.

It is not clear how the report could affect the bill's chances of becoming law. The proposal awaits a vote in the full U.S. House of Representatives. There is no companion bill in the U.S. Senate, but a Miller spokesman said a couple of senators are interested in the measure.

The morale-boosting USO operates 41 welcome centres at U.S. airports, offering soldiers a place to use the Internet, have a snack or play video games. Although it says it didn't ask for the money, it welcomed any help.

"Any dollar amount the USO gets from the American people goes towards the troops and families who need us most," said Gayle Fishel, a group spokeswoman.

(Reporting By Susan Heavey; Editing by Marilyn W. Thompson)

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