Supporters of legislation that Gov. Arnold Schwarzenegger signed last week say it will expand the array of choices people have when they shop for houses. Opponents say it will limit their options.

The new law will require planning agencies to write nonbinding blueprints for slashing planet-warming greenhouse gas emissions from transportation. A failure to devise such a plan could cause a region to forfeit state transportation dollars.

"By giving people a choice to get out of their cars once in a while, we can take a big bite out of our global warming pollution," said Ann Notthoff, a lobbyist for the Natural Resources Defense Council that supports the law.

Lately, say supporters of Senate Bill 375 by Sen. Darrell Steinberg, D-Sacramento, consumers have had little choice but to buy single-family homes far from jobs because of market forces.

Bruce Colbert, executive director of the Property Owners Association of Riverside County and an opponent, counters that the market has built what people want to live in and where. And that, he said, is a home with a backyard for children to play in.

But the law will force many to live in condominiums, Colbert said.

"They're forcing the lifestyle of the single, childless person on the entire populace," he said.

And that's just wrong, said Frank Pluzdrak, an Escondido resident who frequently criticizes "smart growth" projects and maintains government should not be influencing lifestyle choices.

"I think they are stuffing it down our throats," Pluzdrak said. "Neither you, nor I, nor most people, want to live next to most forms of mass transportation."

But Temecula Mayor Mike Naggar said interest in the smart growth concept that calls for building near major transportation lines and job centers is growing.

It also makes sense to encourage more compact housing as long as the door isn't shut on people who want single-family homes, he said.

"When it comes to using a law to social engineer, that's when I have a problem," he said.

The door won't be shut on traditional suburban housing, according to regional planners' read of the law. Rather, it simply will make planners study an array of ideas for reducing the amount of driving people do -- and letting cities and their residents decide whether they are actually going to park their cars.

Bob Leiter, director of land use and transportation planning for the San Diego Association of Governments, a regional planning agency, said the law does not transfer land use authority from cities to regional agencies.

What it does is add a layer of planning for agencies when they rewrite long-range transportation plans every four years, Leiter said.

Having just completed such a rewrite last year, the San Diego County will be due for an update in 2011.

At that time, planners will need to evaluate whether its new long-range plan for roads, trains and buses would serve to reduce driving and help the region meet a target for greenhouse gas reduction set by the state.

If the plan wouldn't put the region on a course for less driving and lower carbon levels, the association would have to write an alternative strategy showing how the target could be reached, Leiter said. But, he said, there would be no requirement to implement that strategy.

"We don't have to enforce that in any way," he said.

And, by just producing such a strategy, San Diego and Riverside counties would avoid forfeiting state transportation funds -- the law's lever.

But Leiter said the process of putting ideas on the table for reducing driving likely will trigger, voluntarily, changes in road planning.

And he said it likely will trigger fewer car trips through telecommuting, four-day work weeks and car pooling.

However, smart growth advocate Duncan McFetridge, president of the environmental group Save Our Forest and Ranchlands, doubts the discussion will translate into concrete actions to reduce driving.

"There is a lot of wiggle room in this bill here for greenhouse gas reduction," McFetridge said. "And the developers and politicians in San Diego County are geniuses at appearing to do the right thing … and in fact sprawling just as they have in the past."

Contact staff writer Dave Downey at (760) 745-6611, Ext. 2623, or ddowney@nctimes.com.