The endorsement by Maurice Dubois on Tuesday was part of a growing push to overhaul the way the state punishes and tracks such criminals.
It came more than a month after convicted sex offender John Albert Gardner pleaded guilty to raping and murdering Amber Dubois and 17-year-old Chelsea King.
The bill co-authored by Assemblymen Pedro Nava and Paul Cook would require people convicted of some sex crimes to carry a driver's license or state identification card identifying them as an offender. The markings could include a distinctive stripe or color.
The strategy is used in two other states. Driver's licenses in Delaware are marked with the letter "Y," and Louisiana emblazons licenses with the words "sex offender."
Cook, a Republican, said the marked licenses could help police in search of missing children. For example, the "alarm bells would go off" if an officer saw a teddy bear in the back seat while checking a driver's license during a traffic stop, he said.
Cook, however, acknowledged a likely battle in the Legislature.
"It's a work in progress," he said. "Something this controversial, you're going to see lots of amendments and changes."
Nava, who is running for state attorney general in the June 8 Democratic primary, said he would be willing to impose the requirement only on people who committed the most serious and violent offenses instead of all registered offenders.
He was unaware of any opposition but anticipated critics would consider it an encroachment on civil liberties. He plans to introduce the bill within days and hopes for a first hearing this summer before the Senate Public Safety Committee.
"We believe it is going to enhance the chances for successful recovery of a child before they are killed or abused," he said. "I think that's a small price to pay."
It's unclear how the measure might have helped Gardner's victims.
In April 2009 -- nearly two months after Amber disappeared and about a year before Chelsea was murdered -- an Escondido police officer cited Gardner for driving with an open container of alcohol and not having a front license plate. But he didn't relay word about the encounter to the detective investigating Amber's case. Police Chief Jim Maher has said he wished the officer had done so.
Nava and Cook have authored a series of bills that also call for a rapid response team in the state attorney general's office to handle reports of missing children and the creation of uniform guidelines on how law enforcement agencies should respond to such reports.
Maurice Dubois announced his support at a news conference. His daughter Amber vanished while walking to school in the San Diego suburb of Escondido in February 2009. She was missing for 13 months before her remains were found.
"What can we do to prevent this from happening again?" Dubois asked. "Try to monitor them, keep track of them, keep them in lockup in cages longer where they need to be. These are predators who are gonna hurt our children."
Carrie McGonigle, Amber's mother, also supports the proposed legislation but said she wouldn't campaign actively for it unless her former husband asks for her help. She is currently helping train volunteers to search for missing children.
Gardner, 31, was sentenced May 14 to life in prison without the possibility of parole.
He had been required to register as a sex offender after a conviction in 2000 for molesting a 13-year-old girl.
Chelsea's parents Brent and Kelly King are leading a campaign for "Chelsea's Law," a bill proposing life sentences for some convicted child molesters and lifetime electronic monitoring of others.
The bill, which cleared its first legislative committee last month, also would ban sex offenders from parks.