Determining the future of closed military bases has led to rancorous land-use battles, but few have been as protracted and divisive as the El Toro Marine Corps Air Station in Orange County, Calif.

Now, after 10 years, four countywide ballots and more than $100 million in costs by vying parties, El Toro is slated for reincarnation as the nation's second-largest municipal park.

For the Navy, which has owned El Toro since 1942, the property's upcoming sale, possibly this summer, will easily be its most profitable since Congress passed the Base Realignment and Closure Act of 1988. It shuttered or realigned about 97 of the military's nearly 500 major domestic bases. In the four rounds of base closures since then, the Navy has brought in $265 million, the most of any of the armed services, and El Toro is expected to exceed that amount.

The payout reflects not only location and size -- at 4,700 acres, it is the biggest military base to go up for public sale -- but the hard lessons of experience, as well.

"Large revenues from land sales were expected in the early days of base realignment and closure, but they never came to pass," said Wayne Arny, the Navy's deputy assistant secretary for installations and facilities.

Arny said the Navy had planned to convey the property at no cost to the county for construction of an international airport, a plan voters narrowly approved in 1994. Backlash quickly erupted from cities worried about increased noise, air pollution and traffic. The controversy was further inflamed two years later when an anti-airport ballot measure -- asking voters to reject the plan without offering an alternative -- was defeated. "The whole issue became a county civil war year after year," said Chris Norby, an Orange County supervisor.

A strong opponent of the airport was the city of Irvine, which realized voters could not support scuttling the airport without having a feasible alternative. Spending $20 million on land-use consultants, lawyers and public opinion surveys, Irvine determined much of the land could become a park.

After a 2000 ballot killed the airport, voters last year approved Irvine's plan for a so-called Great Park.

The plan calls for 3,900 acres of parkland, comprising six major sections. The largest, more than 1,500 acres, will be wilderness and meadowland; the other tracts will house an agricultural heritage park, a veterans memorial park and cemetery, a sports park, a museum and cultural affairs park and fairgrounds. The remaining 800 acres will be sold to developers in an online auction -- by late summer or early fall -- conducted by the General Services Administration (GSA), which is responsible for disposing of government property.

Once sold, the land will be annexed by Irvine and brought under its land-use controls. The buyer must sign a development agreement in accordance with the city's plan, which includes dedicating a portion of the land to the public park. The city expects to raise $200 million in developer fees and $153 million in property taxes from future property owners inside the park's boundaries. Plans call for 3,625 homes as well as commercial and high-tech industrial space.

Funding for museums and other cultural facilities will have to come from private and corporate donations, Irvine Mayor Larry Agran said.

Although the Navy remained neutral throughout the El Toro saga, it took a different tack from past closures, opting to closely collaborate with Irvine rather than look for a quick exit. Indeed, once the park idea took hold, the Navy wanted to sell, but city officials advised patience. Along with annexation, the city will "entitle" the land, which provides all the necessary zoning, thereby sparing developers a costly process. Realizing that entitlement could translate into higher bids, the Navy decided to wait.

"El Toro is unprecedented in the way we worked with the community and in delaying the sale to increase value," Arny said. "We worked with their lawyers; we debated the development; we tried to get more and they tried to squeeze things in. It's been very cooperative."

Arny said that based on the lessons from El Toro, as well as the sale of land at Tustin Marine Corps Air Station in September, also in Orange County, he foresees a bigger role for public sales in the next round of base closures, expected in 2005.

"I think the armed services will be more ready to look at public sales as one method of disposal," he said. "It's better for us and better for the community, because as soon as it's sold it goes back on the tax rolls. If the community gets it, they don't collect taxes until they find a developer."

Tustin's approximately 235 acres sold for almost $1 million an acre at the GSA auction, bringing $208.5 million to the Navy, which puts proceeds from property sales in a cleanup fund for closed bases.

Carol Arnold, deputy director of the property disposal division at GSA's San Francisco office, said the agency will advertise the El Toro property nationally and internationally, using a Web site, fliers, newspapers and presentations to real estate associations. Tours of the property have begun.

Arny and GSA officials prefer not to speculate about El Toro's potential selling price. However, they do not expect to get as much per acre as they did for Tustin because the increased value of entitlement is offset by the fact that the buyer has to donate a portion of the land toward the park.

"Either way, we're not counting our chickens before they hatch," Arny said. Although the Great Park will be 200 acres smaller than Griffith Park in Los Angeles, the largest municipal park in the nation, it is less mountainous and will contain more publicly accessible land, Agran said. In addition, the Great Park will connect several tracts of open space -- the largest two pieces of which are the Laguna Coast Wilderness Park and the Cleveland National Forest -- into one vast protected swath of approximately 590,000 acres.

"The Great Park is the missing link between the coastal hillsides and the inland hillsides all the way down to the Mexican border," he said. "You will have a sea-to-sage interconnected metropolitan open space preserve that we believe will be the largest in North America. With something as spectacular as that, what else could we call it?"

An aerial view of El Toro Marine Corps Air Station shows its empty runways in March 2002. The Navy has owned the 4,700-acre base since '42.