“It’s a very personal way to curry favor with powerful lawmakers,” said Keith Ashdown, the chief investigator for Taxpayers for Common Sense, a watchdog group. “It’s also a lobbying tactic that is not completely understood or even known by the public.”

Several of the defense contractors who contributed to the Johnstown Symphony Orchestra said that they had business ties to Western Pennsylvania and wanted to support community programs there.

“Boeing has always had a strong commitment to the endowment of the arts, both in our nation’s capital and throughout the country,” said Douglas J. Kennett, a spokesman for Boeing.

The disclosure requirement was part of a sweeping ethics rules change adopted by Congress in 2007, after revelations that the House majority leader, Tom DeLay, Republican of Texas, had collected millions of dollars from companies including Exxon and SBC Communications Inc. for his charity for foster children, the DeLay Foundation for Kids, as he ascended the ranks in Congress. Under the law, any time a company or registered lobbyist donates to a charity in honor of a member of Congress, it must be disclosed. There is no limit on how much they can give.

The practice of such unregulated contributions continues to stir controversy. The House ethics committee is currently investigating whether Representative Charles B. Rangel violated any rules by using Congressional stationery when he solicited some $12 million from corporations and foundations for the Charles B. Rangel Center for Public Service at the City College of New York. Mr. Rangel, a New York Democrat, has said he did not seek funds from anyone with business before his committee and merely encouraged potential donors to meet with City College officials.

Critics say that the donations not only allow the givers to build connections to lawmakers, they also create another pool of money for incumbent politicians to dole out and raise their standing among constituents. Many of the charities controlled by members of Congress hand out smaller grants to community groups and local projects. In 2005, Representative Joe Barton, a Texas Republican, established the Joe Barton Family Foundation to support charitable organizations within his district, south of the Dallas-Fort Worth area. The foundation employs Amy Barton, the congressman’s daughter-in-law, as its executive director.

Mr. Barton is no ordinary lawmaker. He has served nearly 25 years in the House and remains one of the most influential members of the Committee on Energy and Commerce.