Orange County facing critical land-use decisions.

Flash forward to the year 2030. Office towers, apartment buildings and high-rise condominium complexes are packed tightly in Orange County's most urban areas. Traffic is a nightmare and houses cost a fortune.

Oh, and there is little land to build on without first tearing something down.

An overly pessimistic scenario? Perhaps. But Orange County is running out of land and the expanding economy is expected to add 734,863 jobs by 2020 - half again today's 1.4 million jobs.

Those new people will need space in which to work and live.

Government and some industry officials point to several signs that the county is capable of handling the expected influx - including office projects coming on line in the John Wayne Airport area and in South County, master-planned communities, freeway improvements and the introduction of toll roads. There's talk about light rail. too.

Still, Orange County is booking up. Eighty-five percent of the county's 510,720 acres is either built upon, not suited for development or set aside for open space, according to the Concord Group, a Newport Beach research and consulting firm. At the normal absorption rate of between 20,000 acres to 30,000 acres a decade, the 75,000 acres left should be built out in 30 years.

For an idea of what Orange County may be confronting in 30 years, consider Los Angeles County. As L.A. grew, people working there searched for affordable housing in the less-urban Orange County. In a sense, Orange County was the Inland Empire of Los Angeles.

Currently, there are about 1,000 new homes for sale in the county and another 60,000 homes on the drawing hoards, according to the Meyers Group and the land brokerage firm O'Donnell/Atkins Co. About 6,600 new homes were sold last year - a rate that would leave the county out of its projected supply in 10 years. That's why analysts say high-rise residential properties could become more common (though only if something is done to prevent construction-defect litigation).

Most of the vacant land that has the potential to be developed is controlled by the Irvine Co. and Rancho Mission Viejo LLC, the combined interests of the Moiso and O'Neill families.

The Irvine Co., in particular, will be the major player. Of the 60,000 homes planned for the county, more than half the lots are owned by the firm, according to a report by O'Donnell/Atkins. That does not include the thousands of acres the firm owns in the eastern portion of Irvine Ranch for which it has yet to reveal its plans.

Irvine Ranch totals 93,000 acres, covering about one-fifth of the county in a horizontal slice across the center from the coast to the eastern hills. Even after having sold off or deeded away close to half of the ranch, the Irvine Co. still owns about 10 percent of all land in the county, or a little more than 50,000 acres.

Of that amount, a little less than half has either been developed or has been designated as permanent open space. Some of the remainder is already slated for development, while the status of other portions is uncertain.

Next in line in terms of !and ownership are the Moiso and O'Neill families, who own about 30,000 acres in the southeastern portion of the county. Under the name Rancho Mission Viejo LLC, the families are developing 4,000-acre Ladera Ranch into an 8,000-unit housing community that will include some retail and commercial development.

They own another 25,000 acres east of Ladera. The future of that land is being worked out with the government under the National Communities Conservation Plan, according to a spokeswoman for the development firm. Part of the goal of that plan is to determine land areas suited for preservation as open space.

With little vacant land, it is difficult to understate the importance of key reuse sites.

The 4,000-acre El Toro Marine Base is one of the largest plots of vacant, or nearly vacant, land left in the county. The airport plan for the site would preclude virtually any commercial or residential development on the site, calling instead for parks, golf courses and open space around the airfield complex. (E&Y Kenneth Leventhal principal Walter Hahn said building homes instead of an airport at El Toro would add two or three years to the housing supply.)

Another major parcel is the 3,510-acre planned South County residential community, Talega. Development is underway for the 4,500-unit housing community planned for San Clemente. Talega is being developed by Catellus Residential Group, Standard Pacific and Starwood Capital Group.

The last of the major parcels is the 1,600-acre Tustin Marine base, set to be turned over to the city next year. City officials have outlined general plans for the property that include 4,518 housing units, a golf course, office space, elementary schools and a high school.

Meanwhile, several high-rises of eight to 12 stories are planned or under construction for the area around John Wayne Airport. That area, as well as the rest of Central and North County, has little vacant land left. Some developed properties containing parking lots and older industrial buildings are likely to be redeveloped to host high-rise office buildings.

A good target for redevelopment is land once used by aerospace firms. Although aerospace firms are still major employers in the county, the players have changed and their land-use requirements have changed over the decades. Boeing Co., for example, recently sold two properties, according to the firm's broker, Rob Socci of Volt Commercial Brokerage. The older buildings on those properties in Anaheim were knocked down to make way for newer buildings.