An updated land-use guide for San Diego County's unincorporated areas would place more homes near existing housing while protecting farmland and backcountry open space, county planners said Friday.

They told the San Diego County Planning Commission that the General Plan provides more flexibility in community planning while allowing for tens of thousands of new homes and protecting the county's important natural resources.

Dan Silver of the Endangered Habitat League said the document, which was first written in the 1970s and has been the subject of an effort to update it since 1998, is the best chance to accomplish those goals.

"This update allows us to change course and presents a town-center model for future growth," he said.

Subject to approval by the Planning Commission and the county Board of Supervisors, the plan seeks to accommodate up to 70,000 more houses in the unincorporated areas.

If that plays out, the county would eventually have about 238,000 residences housing an estimated 663,000 people.

To help preserve remote backcountry open space, the plan proposes shifting about 20 percent of that growth to the county's western regions.

Planners say an overarching goal is to reduce demand on roads, sewer, water, electrical and safety service while maintaining large swaths of pristine land.

Some of the county's 21 community planning groups have raised objections regarding housing density. They don't want increased housing density, because that takes away from their community character.

Commission Chairman Bryan Woods said planners have to reach agreement with the community groups in order for the plan to succeed.

"Many communities are struggling with what should be a minimum lot size, and that needs to be achieved," he said.

In areas such as Fallbrook and Bonsall, the plan could allow several homes per acre, while backcountry lands could be limited to as few as one home per 160 acres.

The Bonsall Community Sponsor Group, which provides planning recommendations to the county, wants larger minimum lot sizes in the plan but has not been specific in what it wants in lot size per home.

Fallbrook wants to make certain that its agricultural uses are preserved along with its village-style architecture in the downtown area.

Rainbow wants a policy that would prohibit any mining activity within that community's planning group area.

Those groups will be heard from when the next hearings take place on Nov. 19 and 20.

Friday's session before the seven-member commission was conducted in two phases: The Department of Planning and Land spent three hours presenting an overview of the chief components ---- land use, mobility, conservation and open space, safety, noise and housing. That was followed by comments from key interest groups.

Commissioners Peder Norby and Michael Beck said preservation of farmlands and backcountry open space is a critical objective.

"We better put a higher value on maintaining agricultural land," Norby said.

That was echoed by Eric Larson, executive director of the San Diego County Farm Bureau, who encouraged the commission to consider allowing people to build homes on backcountry parcels much smaller than 160 acres. Many people are interested in starting small olive groves, for example, but can't necessarily afford to buy such large tracts of land, he said.

Karen Messer of the Audubon Society said the county's openness in developing the plan has been a model of transparency, representing intelligent development that incorporates "smart growth" principles.

But Matt Adams of the San Diego Building Industry Association said a key concern for his group is restricting the number of homes in the backcountry.

He also said a recent county requirement for secondary access roads for new housing as a safety measure is restricting what would otherwise be sensible development.

County planners hope to have the final document before the Board of Supervisors for final adoption by next fall.

See more on the plan, including proposed land-use maps, at http://www.sdcounty.ca.gov/dplu/advance/index.html.

Call staff writer Mark Walker at 760-740-3529.