NEW ORLEANS  The lawyer for one of the four men arrested Monday on charges of interfering with the phones in Senator Mary L. Landrieu’s office in New Orleans said the episode was a prank based on what conservative activists have said was a problem getting through to the senator’s office during the health care debates.

“I think it was an allegation or a rumor about Ms. Landrieu’s office not dealing with phone calls about health reform,” said J. Garrison Jordan, the lawyer for Robert Flanagan, the only one of the four men from Louisiana.

James O’Keefe III, a conservative activist and filmmaker who was one of the men arrested, used a cellphone to record either audio or video in Ms. Landrieu’s offices, witnesses have said. The men’s intentions are not clear, but it is possible they were trying to show the office staff’s reaction if the phone system were disconnected, or to show that the phones were actually working and calls were going through.

“Mr. O’Keefe has a history of trying to embarrass agencies or political entities on camera,” Mr. Jordan added. “I think it was just an ill-designed stunt with no intent to commit a crime.”