A top Democratic aide says Rep. Henry Waxman, a liberal ally of Speaker Nancy Pelosi, is challenging veteran Rep. John Dingell as House Energy and Commerce Committee chairman.

Dingell is the House's longest-serving member. The Michigan lawmaker is an influential supporter of Detroit's automakers.

If Waxman succeeds, he would bring a more environmentally friendly agenda to the committee as it considers global warming and other issues. Waxman and Dingell have battled in the past over clean air laws.

Pelosi and Dingell have had their differences, too. She endorsed Dingell's primary opponent in 2002.

The Democratic aide says Pelosi did not put Waxman up to the move against Dingell. The aide spoke on condition of anonymity because of the sensitive nature of the political fight.

Pelosi and Waxman are from California.