With six weeks to win support for its proposed traffic tax, the Bloomberg administration is trying to sweeten its proposal to charge drivers a fee for using Manhattan’s busiest streets during peak hours. The city is considering offering residential parking permits in certain neighborhoods, curtailing the number of government parking permits it issues to city workers, and offering express bus service in districts where lawmakers oppose the driver fee.

Residential parking permits could be established in Brooklyn Heights, Upper Manhattan, Long Island City, and other neighborhoods surrounding Manhattan’s central business district — a concession to those communities that would discourage drivers from approaching the edges of tolled Manhattan and clogging up their streets to avoid paying the $8 congestion fee.

The city in the past has opposed residential parking permits on the basis that visitors would be unable to find parking. Permit parking has been used for years in cities such as Boston and Washington. In those cities, cars without permits can park for two hours or less.

Another option the city is studying is building “Park and Ride” facilities near train stations, local officials said.

The city’s Department of Transportation is also conducting a block-by-block survey of parking patterns below Canal Street, and studying government parking placard use and abuse, an agency spokesman said.

Eliminating free parking for city employees would take about 19,000 car trips off the city ‘s streets annually, according to statistics provided by the advocacy group Transportation Alternatives. That number represents about a third of the total anticipated reduction in traffic that could be achieved through congestion pricing. A spokesman for the mayor, John Gallagher, said it was still too early to say how many placards Mr. Bloomberg could remove from the streets, or how the city would increase its enforcement.

The Partnership for New York City has recommended to the city that it rein in the number of government parking permits it issues, and enforce that the permits are used only for official government business, the president and CEO of the Partnership, Kathryn Wylde, said.

Cracking down on placard abuse would reduce traffic congestion in Lower Manhattan and could help win the support of the Assembly speaker, Sheldon Silver, who represents the district, sources said.

“Lower Manhattan cannot be one big parking lot for government workers with parking placards,” Council Member Alan Gerson, who represents the neighborhood, said in an interview yesterday. The city currently issues about 150,000 parking placards, which Mr. Gerson said was “far too many for the amount of parking we have available.”

About 37% of government workers drive into the city, as compared with 5% of New York City residents overall. “They’re out of touch with how normal New Yorkers travel,” the executive director of Transportation Alternatives, Paul Steely White, said.

A spokesman said the police department has cut back the number of placards it issues to its staff by about 20% since Commissioner Raymond Kelly was appointed in 2002.