Mayor Bloomberg vowed yesterday to “make the condition of chronic homelessness effectively extinct in New York.”

Mr. Bloomberg’s pronouncement came as he unveiled a five-year plan that he said would cut the size of the city’s 40,000-strong homeless population by two-thirds, prevent chronic homelessness, build 12,000 units of supportive housing, and decrease the time and number of people living in the city’s shelter system.

“It is a persistent, difficult social problem, and – like others we grapple with, like AIDS or drug addiction, it affects far too many of our men, women, and children,” the mayor told the audience at a breakfast hosted by the Association for a Better New York.

“It forces them to live on the margins of society in needless shame. It diminishes them, and in doing so, it diminishes us,” he said.

On Monday night, the most recent night for which the city has statistics, there were nearly 36,600 people living in homeless shelters. Nearly half of them were children.

Mr. Bloomberg wants to change the premise on which the city conducts its homeless services. Instead of seeing it as a necessary component of urban living, Mr. Bloomberg wants to prevent New Yorkers from having to live on the streets.

He wants to reconfigure the city’s outreach services, tailor strategies to particular neighborhoods, and meas ure progress on a neighborhood-by-neighborhood basis in much the same way police now effectively fight crime.

For a mayor who put the fiscal 2005 budget to bed only days ago, the prospect of saving money by streamlining the way the city takes care of its less fortunate is enticing.

If the plan works it could also go a long way toward burnishing Mr. Bloomberg’s credentials as a billionaire mayor who can empathize with his poorest constituents.

The plan could also improve the efficiency of a system that is gobbling up money at a voracious rate. Over the last 10 years, the city has spent $4.6 billion – about 10% of the fiscal 2005 budget for the whole city – on building and maintaining shelters. The budget for the Department of Homeless Services tops $700 million, a 75% increase over 2000.

“Between now and the end of 2009, we must cut the size of the city’s homeless shelter population by two-thirds,” Mr. Bloomberg said. He lauded the city’s efforts to move about 24,000 people from shelters to permanent housing, but said that was not enough. “Money and manpower now used to manage homelessness will instead be devoted to ending it,” he said.

For every dollar spent to prevent homelessness, $3.50 is spent supporting shelter systems. Mr. Bloomberg wants that ratio to change, drastically, over the next five years.

Thousands of individuals and families enter shelters each year without having homeless-prevention assistance that might have saved them from losing the roof over their heads in the first place. Mr. Bloomberg wants to beef up the city’s legal assistance programs so the city might be able to find a way to keep people in more stable housing.

Mr. Bloomberg also envisions a system in which he coordinates various agencies to take a bite out of homelessness. He wants to coordinate releases from jails, prisons, hospitals, and mental health facilities so New Yorkers don’t travel from one agency directly into a city shelter.

The mayor is stealing a page out of the playbooks of some other big cities with major homelessness problems. Atlanta, Los Angeles, and Chicago have also changed their emphasis to preventing homelessness before it starts.

The Homeless Commission in Atlanta has raised $10 million in the past year from private sources to open and operate a new multi-service center where the homeless can get food and showers, help with mental health services, V.A. benefits, and other services, said Crystal Drake, the spokeswoman for United Way of Metropolitan Atlanta, which is helping administer the program.

Another initiative as part of the homeless services overhaul in Atlanta includes sponsoring daycare for homeless women while they look for work, she said.

Advocates for the homeless were generally supportive of the mayor’s plan, although they reserved judgment until the mayor releases further details. Mr. Bloomberg said more specific descriptions of the program changes would be released this summer.

The mayor is fond of saying that his administration has taken the homeless off the street, yet the numbers suggest the problem has gotten worse during his tenure. The population of homeless new Yorkers in municipal shelters has increased 27%. The number of homeless children has risen 63%, according to the Coalition for the Homeless.

They blamed cutbacks in homelessness prevention under the Bloomberg administration and the mayor’s failure to renew a successful city and state agreement to provide supportive housing for the homeless with mental illness.

The Coalition is also critical of Mr. Bloomberg’s expanded use of $100-anight welfare hotels and other for-profit shelter units. It is unclear if the new plan will address that criticism.