Businesses and residential high-rise buildings that throw huge amounts of garbage into bins for disposal have one year to install trash compactors as a new weapon in Chicago's war on rats approved Wednesday by the City Council.

The new ordinance, proposed in April 1999 by Mayor Richard M. Daley, affects properties generating at least 50 cubic yards of garbage per week; the average single-family residence in Chicago produces less than one cubic yard of garbage weekly.

Properties that recycle enough of their garbage to fall below the 50-cubic-yard requirement will not have to install a compactor, though such devices usually end up saving money for their users by reducing the frequency of trash pick-ups.

"Dumpsters often are too easy for rats to enter while searching for food," Daley explained. "Compactors are virtually rat-proof and will help us further reduce Chicago's rat population.

Chicago's rat population is estimated at 500,000, far below the six million rats infesting Chicago 20 years ago. However, Daley's Dumpster Task Force already has closed more than 100 food-selling businesses this year, most for rodent problems that began with overflowing garbage bins.

An estimated 1,400 buildings covered by the new ordinance already have installed compactors, according to Streets and Sanitation Commissioner Al Sanchez. Buildings that prefer not to install one under the new ordinance can opt instead for daily garbage pick-up.

Another element of the ordinance requires food-selling businesses generating more than 1,500 pounds of cooking grease each month to store that material within indoor vacuum containers, which also are rat-proof; this provision of the ordinance also becomes effective one year from passage.