A Petaluma City Council plan to explore the sale of a scenic ranch atop Sonoma Mountain to the state died Monday when Petaluma City Councilman Clark Thompson withdrew his support for the project.

Thompson's reversal puts the future of the 270 acres back in limbo after a 12-year effort to open the space as a park. But supporters vowed Monday to make the park an issue in the November campaign.

Petaluma, which has owned Lafferty Ranch since 1959, has sought since 1992 to open the land to hikers as a nature preserve. However, the city has run into roadblocks put up by rancher Peter Pfendler and other property owners near the ranch.

The idea of selling the ranch to the state is intended to build on longstanding plans to create a network of trails and parks atop the mountain and to bring the state's power to bear against park opponents.

In May, Thompson had voted in favor of talking to the state about buying the ranch. However, he later asked the City Council to reconsider the resolution authorizing the talks, saying he wanted to suggest some changes.

Monday, Thompson wanted to rescind the resolution, saying he had gotten negative feedback about the plan from some state officials.

"We need to get all citizens behind this before we move forward," Thompson said. He suggested a council subcommittee or citizens' panel be formed to look into the issue.

Following the City Council's May vote to approach Sacramento, a state parks official indicated the state couldn't afford to be interested, but might be open to reconsideration. But Board of Equalization Chairwoman Carole Migden, who also is a leading November candidate for the North Bay state Senate seat, has expressed support.

Council members Mike Harris, Bryant Moynihan and Mike O'Brien joined Thompson in rescinding the resolution.

Councilman Mike Healy said Thompson's talk of a citizens' committee was just window dressing for killing the resolution.

"I'm very disappointed," said Healy, who supported the effort to approach the state.

A delay in talks with the state on Lafferty Ranch will mean the possible loss of state funding to buy the land, Healy said.

Healy chastised Thompson for discussing the matter privately with state officials instead of asking them to come before the council.

Healy urged the council to consider forming a citizens' panel on Lafferty Ranch at its next meeting and to set a two-month deadline for it to report back to the council.

Will Stapp, founder of the group Residents for Lafferty, called Thompson's action a "shameful reversal of public policy."

Larry Modell, chairman of the political group Petaluma Tomorrow, said the park now is likely to become a campaign issue because its opponents have made it into one.

Moynihan, O'Brien and Torliatt's seats are up for election in November. Thompson temporarily is filling a council vacancy while Councilman Keith Canevaro serves with the Marines in Iraq.