Mayor Michael Bloomberg on Thursday announced plans to reduce the number of city-issued parking placards _ which allow people to park in prime spaces off limits to other drivers -- and crack down on counterfeit and misused cards.

For years critics have blamed the Big Apple's clogged streets, among the world's most congested, and the dearth of curbside parking spaces in part on the seemingly widespread use and abuse of the placards, small cards that are placed on the dashboard and let traffic agents know that a vehicle has special privileges.

The mayor demanded each city department reduce the number of parking placards it issues by at least 20 percent by March 1.

Only the police and transportation departments will have the authority to issue the placards. Currently, various city agencies, including the fire and education departments, can authorize them.

Also, the police department will create a special unit to go after people who use fake or unauthorized placards, and agencies will devise procedures to prevent abuse among city employees, the mayor said.

"Parking placards are a necessary tool for conducting city business,'' Bloomberg said, ``but we have no tolerance for their abuse, which contributes to congestion. City workers have often led by example, and our efforts to reduce traffic congestion will be no different.''

There are about 70,000 city-issued parking placards, a spokesman for the mayor said. The figure doesn't include cards issued by state and federal agencies nor counterfeit ones; city officials plan to try to determine that number.

The placards often alleviate drivers' frustrations at finding legal parking spaces, allowing them to sometimes park in "No Standing'' and "No Parking'' areas or in card-designated spaces, particularly near city buildings.

Under the new plan, the police department will give out placards for its employees and other law enforcement agencies; the transportation department will issue cards for other city departments. City officials plan to give closer scrutiny to how many, if any, placards each city department needs.

Some applauded the mayor's plan. The Straphangers Campaign, a commuter advocacy group, said the plan, if successful, would lead more people to use subways and buses. The group suggested officials begin using new permits that can be checked electronically by traffic enforcement authorities. It also said the number and holders of permits should be made public.

Transportation Alternatives, a nonprofit advocating people drive less and walk, bike and use buses and subways more, said the mayor's plans were long-overdue reforms. The "unchecked abuse'' of placards has "exacerbated'' congestion, the group said.

"This is a big step, not just in the direction of good government but towards less-congested streets,'' said Paul Steely White, the group's executive director.

The group encourages people to report misuse of parking placards at the uncivilservants.org Web site.

Bloomberg continues to encourage people to use buses and subways instead of driving to reduce carbon emissions, traffic congestion and the demand for curbside parking.

Last April, he unveiled a so-called congestion pricing plan as part of his goal of a greener New York. It includes charging motorists $8 to drive into the busiest parts of Manhattan on weekdays between 6 a.m. and 6 p.m.; truck drivers would pay $21.

The mayor and the state Legislature set up a commission to examine the congestion pricing and other ways to reduce traffic. The commission has until the end of January to recommend a plan, which will then go to the Legislature and the City Council.