IRVINE, Calif., June 28 — It had always seemed a given that once the residents of the vast suburban stretches of Orange County decided what the shuttered El Toro Marine Corps Air Station here should become, a decade of epic battling would end and the workaday task of drawing up plans and calling in the earthmovers would begin.

That decision came in March, when voters soundly rejected plans for a big new airport in favor of what has long been called the Great Park. Though there is still some legal skirmishing, the park the voters selected would fill a great part of the 4,700-acre site, a billiard-table-flat collection of deserted runways smack in the center of the county. Many here say it would become America's greatest urban park.

But now, as planners try to figure out how to build and pay for the park, and lawmakers wrangle over the details, it is starting to look as if the political battle was the easy part.

"I would say one book is written now in this story, but it's going to be more than one book," said Todd Spitzer, a county supervisor who fought against the airport for years. "Another book is going to be written about what happens with that 4,700 acres. We just haven't had time to focus on that part yet."

Many expected the Navy to give the land to the county at no charge, as the military has sometimes done in other base closings. But the Navy decided to sell it in pieces to the highest bidders, collaborating closely with local governments.

The sales could net more than $1 billion and have a profound impact on Orange County, which has nearly three million people and is often described as a collection of suburbs in search of a downtown.

Given the new economics of the site, local planners are preparing to allow developers to build on perhaps two-thirds of the old base, with projects including a university campus, an industrial park and golf courses surrounded by homes.

What will be left for the promised park? Perhaps 350 prime acres where abandoned runways now sit.

"What we all campaigned for was to have a Great Park," Mr. Spitzer said. "But it's not going to be a great big park. The economic developments are going to drive how much open space there will be. The land use will be driven by the economics."

Larry Agran, mayor of the City of Irvine, which is next to El Toro and is expected to annex the land, said, "Well, it's a development plan with the idea of a Great Park."

There is another complication. Residents of the poorer, more densely populated northern half of the county are demanding that some of the revenues generated by private development be used to build smaller parks in their area.

"I think if it's done right the entire county would benefit and tourism would benefit," said John Palacio, president of the school board in Santa Ana, an overwhelmingly Latino working-class city just to the north. "Some of that money must be used to build parks in our area, too."

Cynthia P. Coad, another county supervisor, has threatened to stop Irvine's annexation of the base and construction of the park unless the planners promise that $800,000 a year will be dedicated to creating parks in the north. "I'm not interested in megaparks," Ms. Coad said. "I want neighborhood parks in the heavily built up areas of the north county."

Irvine's city manager, Allison Hart, has been working closely with the Navy to draw up a sales plan that will include a master plan for how the properties can be developed once they are sold to private companies.

Irvine's plan looks far different from what residents voted on in March, when 3 percent of the base site would have been turned over to private developers, leaving 97 percent for various public purposes.

The new plan involves giving developers 18 percent of the land and leaving 82 percent for public park space, which would include convention centers, educational campuses and the like. Private money would finance all the development.

As conceived now, there would be a 1,000-acre natural habitat on the northern end of the land, close to 300 acres of agriculture, some of which would be a prison farm, a 75-acre cemetery (the first in Irvine), 45 holes of golf, more than 400 acres of housing (25 percent of which would have to be for low-income residents) and several hundred acres of industrial and commercial development.

The 350 acres of park would lie in the middle, divided by some creeks.

Daniel Jung, Irvine's director of strategic programs, said the site might include some housing planned in the almost-freakish expectation, for California, that people would be close enough to public transportation and shopping that they would not use their cars every day.

"It's a development you haven't really seen in Orange County," Mr. Jung said.

Some officials have insisted that the park would vault Orange County into the nation's first ranks. But while people here often cite other major urban parks in the region as models, it is clear that the comparisons come up short.

For instance, Balboa Park in San Diego, the park most often cited, is just 1,200 acres, but it is in the middle of a dense urban setting. It is home to 15 museums, the San Diego Zoo and a theater.

North of Orange County is Griffith Park, near the heart of Los Angeles. It consists of 4,107 acres of mountainous wilderness and only a modest amount of development. There is the Los Angeles Zoo, the Autry Museum of Western Heritage, a theater, an observatory and lots of sports fields, but mostly heavily wooded hillsides and canyons.

The El Toro site is flat, a big chunk of it covered with asphalt from the old runways. It is surrounded by suburban development and a clean-looking, high-tech industrial park.

"It's hard to know what the draw would be," said Con Howe, the planning director for Los Angeles. "It's not surrounded by dense urban development. It's suburban. It's not an immediate area that is open-space-starved. And it does seem like from the get-go they have no natural character there to work with."

Ms. Hart, the Irvine city manager, suggested that those opinions miss the point.

"This is a total free-market experiment," Ms. Hart said. "We want to take a little more time to package this and then it's rock 'n' roll."