Los Angeles City Councilmen Ed Reyes and Eric Garcetti have worked for months to promote a citywide mandate that virtually every new housing development include some units that are affordable to people of low or moderate income. It's been a tough sell. Many private developers remain dead set against it, and at public hearings this month they are hoping to pick up an ally: neighborhood councils.

Developers and neighborhood groups more typically take opposite sides in planning battles, L.A.'s explosive growth having spawned a backlash of NIMBYism. What is expected to unite them on the proposed policy, known as inclusionary zoning, is many residents' unease with low-income housing. They think of slums, crime and big public housing projects, not a house or condominium that from the outside looks no different from the higher-priced one next door.

Los Angeles desperately needs housing that schoolteachers and police officers, waiters and nurse's aides can afford. Many nonprofit groups tap government grants to build such housing and cover the costs of renting or selling at below-market rates. Inclusionary zoning would supplement those efforts, but without public subsidies.

That, of course, is why developers don't like it. Forced to cover the costs themselves, they argue, they would have to raise the prices on the other units. And Los Angeles already has too many regulations, builders complain; many say they will stop building here if they are faced with more.

Developers, of course, are businesspeople, not philanthropists. Key to making inclusionary zoning work is providing incentives to offset the developers' costs, as is done in Santa Monica, West Hollywood, Pasadena and about 100 other California cities with inclusionary laws. A city, for example, might let the developer build more units than usually allowed so that income from the additional apartments would make up for losses from the lower-priced ones.

Here's where the neighborhood councils come in again. Wary of increasing traffic or congestion, they probably will oppose extra units or cuts in the number of parking spaces. The City Council members who support inclusionary zoning will have to persuade neighborhood groups that affordable housing doesn't mean instant slums and that higher density will work in carefully planned areas, such as around public transportation lines.

Doing so will certainly test the City Council's negotiating skills. At the same time, tackling this admittedly complex proposal will test the neighborhood councils' willingness to offer guidance beyond the reflexive "no" that many expect.