Ric Francis / AP Former astronaut Buzz Aldrin, right, appears with X Prize Foundation and Google officials to announce the spaceflight contest Thursday.

The battle over liquefied natural gas off the Ventura County coast revved up again Thursday with opponents and proponents squaring off over a new proposal.

Earlier this year, state and federal officials rejected plans by Australian mining firm BHP Billiton to build a floating platform that would accept liquid natural gas.

This time, Houston-based NorthernStar Natural Gas wants to turn a shuttered oil rig platform 12.6 miles off the coast of Oxnard to receive chilled natural gas, convert it to vapor and pipe it ashore. The company has named the proposed site Clearwater Port.

On Thursday, NorthernStar took about 115 people out on a boat ride to see the platform and watch whales. Less than 50 feet away from where the boat was docked at the Ventura Harbor, about 25 opponents waved signs and decried the company's Clearwater Port project.

Critics said it would hurt marine wildlife in the nearby Channel Islands National Marine Sanctuary, disrupt shipping and recreational boating, pose a security threat and possibly be damaged in an earthquake. They also questioned the need for liquid natural gas.

A company official said he understood the need to question the project. But it's too soon to say what the effects will be until a draft environmental study is complete in early 2008, said Joe Desmond, NorthernStar's senior vice president of external affairs.

California must address its natural gas supply to keep power affordable and abundant, he added.

The Golden State imports 87 percent of its natural gas and faces stiff competition from East Coast states for Rocky Mountain supplies, said Desmond, a former energy official in Gov. Arnold Schwarzenegger's administration.

Billiton's proposal largely fizzled under concerns over air pollution and increased greenhouse gases.

In the midst of state hearings earlier this year, NorthernStar announced that Clearwater Port would comply with Ventura County's air quality standards.

New technology will heat the gas using ambient air temperatures, helping reduce pollution, said Billy Owens, NorthernStar's vice president of West Coast development.

According to a published report, the company's application for a state and federal permit identified structural deficiencies in the oil rig platform. Desmond called them "minor," adding that NorthernStar must retrofit the facility to current structural standards.

If air quality appears to be less of an issue, critics say they are still opposed to the facility. The need for natural gas in California has diminished because a new facility will open soon in Baja Mexico, said Linda Krop, chief counsel of the Environmental Defense Center.

Carmen Ramirez of the No LNG Community Alliance said opponents will focus on engaging the community from Santa Barbara to Malibu to defeat the proposal.

"We're going to make sure this is not going to happen," Ramirez said of NorthernStar. "You might as well go home."