A City Council slush fund that held millions of dollars is drying up, thus curtailing the influence council speakers will be able to exert over their members.

The end of the long-standing practice of stashing away money in the city budget by hiding it behind fictitious organizations is leaving Speaker Christine Quinn and her successors without a discreet pot of money to reward political allies and favored organizations.

“The fewer the amount of goodies that can be distributed, the less the power,” a professor of political science at Baruch College, Douglas Muzzio, said. “Legislative leadership involves carrots and sticks. These are some big juicy carrots that will no longer be available.” The council’s practice of making it appear that millions of dollars have been awarded to phantom groups and then allocating the money to legitimate organizations later in the year is being investigated by the U.S. attorney’s office and the city’s Department of Investigation.

Ms. Quinn, a likely candidate for mayor, said last week that she ordered the practice to stop last year, but that her directive was ignored. During Ms. Quinn’s two years as speaker, $4.7 million had been earmarked for fake groups. A City Council member who is running for mayor and has been a longtime critic of Ms. Quinn, Tony Avella, said the slush fund allowed the speaker to dole out favors and promote her political agenda. Without it, he said, her power would be put in check.

She would retain the ability to give out favors, but it “just won’t be as easy,” he said. “It’s not like you can all of a sudden find money.”

Ms. Quinn can influence her members through the assignment of committee leadership positions, which can come with pay raises of several thousand dollars; the movement of legislation, and money from the budget for organizations or projects in a council member’s district.

The president of Air America Radio, Mark Green, who ran against Mayor Bloomberg for mayor in 2001, said the end of the slush fund would only marginally reduce Ms. Quinn’s influence “because she has so many other levers.”

He said disclosures about the budgeting practice are “a serious problem for the speaker because critics could say she either looks incompetent or untruthful.”

Some political observers have said they don’t understand how the council’s bookkeeping trick hadn’t been discovered by the mayor’s budget office, where a former director of the council finance division now works.

Mr. Bloomberg said yesterday that his staff vets every organization before it sends out checks.

“In these cases, checks were never sent out, I gather, so, you know, the investigation is still continuing, so we’ll have to see,” he said.