NEW YORK CITY ? Hundreds of homeless people living in encampments under highways and bridges and next to train trestles will be aggressively urged to leave the streets, Mayor Michael Bloomberg said Monday.

The city’s Department of Homeless Services has found 73 areas – difficult to reach and mostly out of sight – where some 350 homeless people have set up encampments and communities. The majority are in Manhattan.

Outreach workers will “humanely, respectfully and firmly” encourage them to stop living on the streets and take advantage of city services like housing assistance, substance treatment programs and shelters, the mayor said.

An estimated 3,800 people live on New York’s streets and in its subways, according to 2006 figures from the city’s annual homeless head count. Officials say the number dropped from last year’s 4,400, and Bloomberg has set a goal of reducing it to 1,465 by the time he leaves office in 2009.