HILO, Hawai'i — Mauna Kea on the Big Island is the best and least-expensive site for NASA's Outrigger Telescopes project, and the space agency still wants to put the $50 million stargazing project there, according to a record of decision released yesterday.

However, NASA reserves the right to move the project to a less-desirable site in Spain's Canary Islands if it can't be built on Mauna Kea, according to the decision.

The decision completes the environmental impact statement process NASA began in 2003, but the project is still being reviewed by the University of Hawai'i's Office of Mauna Kea Management, and still needs the approval of the UH Board of Regents before it can proceed.

To date, opponents of the Outrigger telescopes have filed a federal lawsuit against it, and battled the project in a contested-case hearing before the state Board of Land and Natural Resources. Another lawsuit challenging a state conditional use permit for the project is pending in Hilo Circuit Court.

Critics have said the 13 observatories on Mauna Kea have had a major impact on the sacred mountain's cultural resources, and the authors of NASA's environmental impact statement agreed.

However, the EIS concluded the relatively small additional Outrigger telescopes would have a little additional impact, and the document outlines $2 million the space agency plans for preservation and protection of historic and cultural resources on Mauna Kea in connection with the project.

The agency plans steps to protect the wekiu bug, which lives in the summit area and is a candidate for listing as an endangered species.

Opponents also have worried about potential damage to the mountain's water supply, the effect on any area burial sites, and interference with Hawaiian cultural practices.

Despite the years of delays, Rolf Kudritzki, director of the University of Hawai'i's Institute for Astronomy, said he expects NASA will press ahead to put the project on Mauna Kea because the 13,796-foot mountain "is just simply the best astronomy site in the world."

"I am really convinced that it will be done on Mauna Kea, but I'm always an optimist," Kudritzki said.

The Outrigger project involves interferometry, which combines the light-gathering abilities of more than one telescope to sharpen the images astronomers can gather from deep space. The sharper images aid astronomers in their search for planets orbiting distant stars.

The most obvious advantage Mauna Kea holds over the Canary Islands is the existing twin 33-foot W.M. Keck Observatory telescopes there, which are the largest and most powerful in the world.

The Outrigger project will allow scientists to combine the Keck telescopes' observation powers with up to six new six-foot Outrigger telescopes.

If approved, construction would begin this year or next, and the new telescopes would start operating in 2007.