The Santa Susana Field Laboratory, a former rocket engine and nuclear test site in the hills south of Simi Valley, will be transferred to state ownership and placed off-limits to development if officials accept a tentative agreement announced Friday between the state and the property's owner, the Boeing Co.

The potential transfer is part of a complicated deal announced as Gov. Arnold Schwarzenegger signed a bill that requires Boeing to clean the 2,849-acre site to the highest standards of the U.S. Environmental Protection Agency before the property can be released for development.

"I am pleased to announce this historic agreement will benefit the environment, nearby residents in Ventura County and the people of California," Schwarzenegger said in a prepared statement.

The bill, SB 990, was written by Sen. Sheila Kuehl, D-Santa Monica. Its passage in the Assembly last month capped a six-year legislative battle to ensure strict cleanup standards are used at the field laboratory, which has both chemical and radioactive contamination.

The tentative agreement was signed by Boeing, the state Environmental Protection Agency and the state Resources Agency. It requires Boeing to enter into a binding agreement with the state that calls for the land to be cleaned to "levels acceptable for residential use and that protect individuals living in the vicinity of the property."

The agreement would also mandate that Boeing release the land to the state once it is cleaned up. The site would then be used for park, recreational and open space.

Once the binding agreement is reached, Kuehl will carry a bill in the next legislative season that, if passed, would void the portions of SB 990 that call for the Santa Susana Field Laboratory to be cleaned to Superfund standards before it is released by Boeing.

On Friday, Kuehl said in an interview that permanently protecting the land from development was a good thing, as was mandating a cleanup standard that protects area residents.

The tentative agreement, however, does reopen the discussion of what standards will be used to clean the contamination at the site.

"I have done my very best to remind the people of the state and up to the governor's office, that if the state is going to accept it as parkland they need to worry how clean it is," Kuehl said. "It does not need to be what Boeing is already doing."

The tentative agreement between the state and Boeing capped months of negotiations as environmentalists, community members and nuclear watchdogs successfully lobbied lawmakers to support SB990.

Assemblywoman Julia Brownley, D-Santa Monica, who helped shepherd the bill through the Assembly, said Friday that it would be hard to predict the level of cleanup the state and Boeing will agree to.

"It can be years before it is determined as part of this agreement," she said. "The one very positive thing is that this property will never be residentially developed."

Kuehl's bill garnered bipartisan support, including that of Assemblyman Cameron Smyth, R-Santa Clarita, whose district includes part of Simi Valley. Smyth announced Friday that he has started work on creating a state park on the land.

Boeing officials began looking into the possibility of turning over the land nearly two years ago, spokesman Dan Beck said. "We approached state officials and asked, How can we make this happen?'" he said.

One of Boeing's most outspoken critics on the cleanup of the Field Laboratory, nuclear watchdog-group leader Dan Hirsch, lauded Kuehl's work on the bill but was skeptical about the future agreement.

"Since we have such a history of Boeing breaking its promises and since this promise is vague, we will watch very closely the final, as yet to be written, agreement," Hirsch said. "If Boeing breaks its promise we will vigorously oppose any amendment to weaken the bill."