Sen. Arlen Specter helped direct almost $50 million in Pentagon spending during the past four years to clients of the husband of one of his top aides, records show.

Specter, R-Pa., used a process called "earmarking" 13 times to set aside $48.7 million for six clients represented by lobbyist Michael Herson and the firm he co-founded, American Defense International. The clients paid Herson's firm nearly $1.5 million in fees since 2002, federal lobbying records show.

Herson's wife, Vicki Siegel Herson, is Specter's legislative assistant for appropriations. She deals with Specter's work on the Senate Appropriations Committee and its defense subcommittee, where all the earmarks originated. Siegel, who uses her maiden name at work, is a former lobbyist for defense contractors who has worked for Specter since 1999.

In a statement responding to questions from USA TODAY, Specter said he did not know the earmarks were going to clients of Siegel's husband. "I am advised that at no time did her husband lobby my office or seek appropriations from any member of my staff," the statement said.

"Even when there is nothing improper about the actual earmark, it's very difficult for citizens and even other members to be sure," said Dennis Thompson, who teaches ethics at Harvard University.