In Republican circles, Christopher J. Ward was the go-to guy for politicians who needed help managing their campaign finances. As a staff member at the National Republican Congressional Committee and its treasurer since 2003, Mr. Ward was so valued that more than $360 million in donations to the committee passed through his hands — with few questions asked.

His reputation as someone who could balance books and fill out complicated regulatory forms was such that word of Mr. Ward's skills spread.

Eventually, he was named treasurer for 83 other Republican committees, including leadership political action committees for members of Congress and campaign committees for prominent Republicans. He regularly managed the finances of presidential dinner fund-raising committees, and was even a partner in a private company that advised politicians on complying with federal campaign finance laws.

But what none of his clients knew, investigators say, was that Mr. Ward may have had his hands a little too close their money.

He is now the focus of a Federal Bureau of Investigation inquiry prompted by the disclosure of the National Republican Congressional Committee that hundreds of thousands of dollars was missing and presumed stolen by Mr. Ward, who was fired from the committee in January.

Investigators are examining what may have been a sophisticated embezzlement scheme involving forged audits and multiple wire transfers from political groups to Mr. Ward's personal bank accounts.