LOS ANGELES -- A plan allowing private investors to pay for and extend the Metro Purple Line subway under Wilshire Boulevard to Santa Monica moved forward Thursday with the full support of the Metro Board of Directors.

Los Angeles Mayor Antonio Villaraigosa, who is a member of the board, introduced a motion that would establish a public-private partnership to pay for 23 identified-but-unfunded mass transit projects. During the next two months, Metro officials will solicit concepts and preliminary proposals for funding. That information will then be reported to the Metro Board of Directors by July.

Since taking office nearly three years ago, Villaraigosa has repeatedly touted the "Subway to the Sea" as an alternative to the congested traffic on Wilshire Boulevard. The subway does not extend west of Western Avenue because of federal legislation that banned tunneling under Wilshire over concerns of methane explosions. Late last year, new legislation repealed that ban.

"It's time to recognize that the only true long-term solution to gridlock is an efficient, convenient mass transit alternative. It is time to get serious about investing in rail again," Villaraigosa said.

"And just as our national leaders need to prioritize transportation funding to meet the challenges of today, so too must our state and local governments. We need to think differently about how we provide the transit solutions our region urgently requires."

Proposals must assume that Metro employees, and their designated unions, would operate and maintain the rail systems.

Public-private partnerships may also be used to expand light rail systems and busways. In amending the motion, Long Beach City Councilwoman Bonnie Lowenthal, also a Metro Board member, asked that the second phase of the Metro Gold Line Eastside Extension and Long Beach (710) Freeway improvements be considered for public-private partnerships.

Extending the subway could cost at least $5 billion -- making it Metro's most expensive transit line -- and take a decade to build. Last summer the Metro Board agreed to spend $3.6 million and 18 months to study the feasibility of extending the Purple Line to Santa Monica.

Los Angeles County Supervisor Mike Antonovich, also a member of the Metro Board, has been a vocal opponent of the subway expansion, arguing that it would be too costly and drain resources from other county rail systems.

Los Angeles County does not have any privately funded transit systems. Similar financial structures have been used to expand the London Underground and Canada Line.