Armed Services Committee Chairman Ike Skelton, D-Mo., had just finished addressing his Republican colleague Todd Akin Thursday.
Skelton then turned to the side and muttered "stick it up your ass."
The comment was just audible on the C-SPAN tape of the proceedings and was not included in the Congressional Record, the official record of speeches on the House and Senate floor.
Skelton's spokeswoman, Jennifer Kohl, said the comment was not intended to be broadcast and was "said out of frustration in the heat of debate." She said Skelton, a veteran lawmaker known for working well with Republicans, planned to apologize to Akin.
The dispute arose over opposition from Akin and other Republicans to inclusion in a major defense policy bill of a provision extending federal hate crimes law to include violence against gays.
Akin, a member of the Armed Services Committee, had spoken before Skelton, saying the hate crimes measure was "poisonous enough in fact that we refuse to be blackmailed into voting for a piece of social agenda that has no place in this bill."
Skelton, in his on-mike reply, said he wanted "to remind my fellow Missourian" that the Senate had voted for the defense bill, with the hate crimes provision, by a vote of 87-7.
Akin's spokesman, Steve Taylor, said the remark was "shocking and not characteristic of Skelton's behavior." He said Akin, who has a son going to Afghanistan in three weeks and is normally a strong supporter of defense legislation, was "very disappointed in the personal digression."
National Republican Congressional Committee spokesman Tom Erickson issued a statement that "Skelton needs to apologize, not only to his colleagues in the House, but also to his constituents who shouldn't have to put up with this sort of behavior from their elected representatives."
Both parties have complained recently about the lack of civility in the House, the Democrats after Rep. Joe Wilson, R-S.C., yelled out "you lie" during a speech by President Barack Obama on health care legislation, and Republicans after Rep. Alan Grayson, D-Fla., said on the House floor that the GOP approach to health care reform was telling old people to "die quickly."