The position was created in 1967 to act as an advocate for the state's natural resources. Republicans eliminated the office in 1995, believing it had unfairly targeted businesses with expensive lawsuits.
Richards, a state representative from Milwaukee, said Tuesday restoring the office would honor Wisconsin's tradition of valuing natural resources.
Dane County District Attorney Ismael Ozanne and Jefferson County District Attorney Susan Happ also are vying for the Democratic nomination. Their campaigns didn't immediately return email messages.
The only Republican running for attorney general is Waukesha County District Attorney Brad Schimel. His campaign also didn't immediately return an email.
Incumbent Republican Attorney General J.B. Van Hollen isn't running for re-election.