Honolulu officials expect to decide within a month whether a major new garbage-to-energy plant will be built to help alleviate O'ahu's growing garbage problems.

Such a facility could dramatically reduce the amount of trash that goes into the controversial Waimanalo Gulch landfill near Kahe Point, but it would take years to build and likely cost hundreds of millions of dollars.

Meanwhile, a key ruling on the landfill's future could come in a week. The nearby Ko Olina resort and state Senate President Colleen Hanabusa have asked the city Planning Commission to reject a two-year extension of the landfill's operating permit, which expires in May. The plan also would require approval from the state Land Use Commission.

As the expiration date draws closer, the city expects to soon decide how it will request offers from companies that hope to ship some of the island's trash to a Mainland dump.

"I think we're pretty close," city environmental services director Eric Takamura said. "Within two weeks, we should have a package ready."

It would likely be several months before any trash-shipping deal could be finalized, however, and such an arrangement wouldn't eliminate the need for a landfill here, Takamura said.

The plan will call for shipping away at least 100,000 tons of trash each year, he said.

More than 300,000 tons go into Waimanalo Gulch each year, along with 168,000 tons of ash and residue from the H-Power garbage-to-energy plant.

H-Power burns about 600,000 tons of trash, and a new plant could handle 400,000 tons more.

Three companies submitted proposals last year that could include a new plant, but details are being kept confidential.

The city sought offers to build and operate a new plant, modify and operate H-Power for 20 years, or a combination of both.

H-Power burns trash to heat two huge boilers, which produce steam that powers a turbine and generates up to 46 megawatts of electricity.

The new plant could be based on a different technology, such as gasification or vitrification, which burn waste at higher temperatures and leave less ash but could be more expensive to build and operate.

Covanta Energy Corp., which now operates H-Power, has confirmed that it is among the bidders, but the structure of the offer remains secret. The company's H-Power operations contract expires in 2010, and it hopes to continue beyond that year.

Former Mayor Jeremy Harris had long pushed to add a third boiler to H-Power so it could handle an additional 120,000 tons of trash each year. But the plan became bogged down while the City Council questioned the financing and called for a plant based on an alternative technology.