The move comes after Riordan's Save Los Angeles campaign determined it would not meet its own Dec. 28 deadline to gather signatures to get pension reform on the May 21 ballot.
Riordan's plan would move new city employees to 401(k)-style retirement accounts. He says rising pension costs will deplete taxpayer money from other essential city services.
Riordan launched his campaign earlier last month and says he has spent between $200,000 and $400,000 of his own money on the initiative, which included paying about 500 signature gatherers.
His plan has been met with fierce opposition from public employee unions, including the Los Angeles Police Protective League and Mayor Antonio Villaraigosa.
"I have long appreciated Mayor Richard Riordan's love for the city of Los Angeles and his efforts to keep it strong. Most people concluded, however, that his pension reform proposal went too far and would have cost the city more money than the current system," Villaraigosa said.
LAPPL President Tyler Izen called Riordan's plan "simplistic and costly for taxpayers."
"We appreciate Mr. Riordan's concern for the city's financial status, we just disagree that this Charter change was a viable option," Izen said. "As I have said from day one, thoughtful analysis and real solutions are needed to address pension issues, and the League will continue to work towards those solutions with the city or anyone else who wants to roll up their sleeves and help."
Villaraigosa has instead designed a more modest pension reduction plan, already approved by the City Council last month. The plan raises the retirement age for newly hired city workers from 55 to 65 and caps cost-of-living salary increases at 2 percent. The city will also stop covering the retirement health care costs of spouses and use a three-year average to calculate retirement payouts in order to prevent pension "spiking."
City budget analysts expect the plan will save taxpayers $30 million to $70 million over the next five years and $4 billion over 30 years.
City News Service contributed to this report.