The government said Halloran, 42, told the undercover agent that he wanted to get his "mortgage situation resolved" and to be named deputy police commissioner if Smith were elected mayor.
Halloran's attorney, Dennis Ring, said: "The councilman denies all allegations and looks forward to clearing his name and returning to court."
On Tuesday evening, Halloran was stripped of his committee assignments and money-allocating authority in the City Council. The Queens Republican Party said in a statement the chairman has asked Tabone to resign from his position, pending the outcome of legal proceedings.
Representatives for Savino and Tabone did not immediately respond to requests for comment.
In court papers, the FBI detailed numerous meetings over the last year among the defendants, the undercover FBI agent and the cooperating witness, who pleaded guilty to federal charges last month in a deal aimed at winning leniency at sentencing.
In a Jan. 25 meeting in Smith's car in Rockland County, the cooperating witness told Smith that buying the help of Republican county committee leaders would cost "a pretty penny" and asked if it's "worth any price," the complaint said. The FBI said Smith responded: "Look, talk to me before you close it. But it's worth it. Because you know how big a deal it is."
If convicted of conspiracy, wire fraud and violation of the Hobbs Act, Smith could face up to 45 years in prison. If convicted, Halloran could face the same potential penalty on charges of conspiracy and two counts of wire fraud. Tabone and Savino were each charged with conspiracy and wire fraud, which carry up to 25 years in prison.
Besides the mayoral plot, authorities said the investigation also revealed a scheme in which Halloran received $18,300 in cash bribes and $6,500 in straw donor campaign contribution checks to steer up to $80,000 in City Council money to a company he believed was controlled by those who paid him the bribes.
In a third plot, prosecutors say, Spring Valley Mayor Noramie Jasmin, 49, and Spring Valley Deputy Mayor Joseph Desmaret, 55, agreed to accept financial benefits so that Smith could use his power as a senator to help obtain state funds for road work in the Rockland County village outside New York City that would benefit a real estate project that Smith believed was being built by the undercover agent's company in Spring Valley.
Jasmin and Desmaret also were arrested Tuesday. Jasmin and Desmaret were charged with mail fraud, which carries a potential penalty of 20 years in prison.
Representatives for Jasmin, and Desmaret did not immediately respond to comment requests.
The defendants were all released Tuesday on a $250,000 bond.
Several civics groups have called for campaign finance reform following the arrests. Representatives for Fair Elections for New York, Common Cause and the Brennan Center for Justice are holding a press conference Wednesday to urge "comprehensive campaign finance reform."
Barr reported from White Plains. Associated Press writers Jennifer Peltz and Tom Hays in New York and Michael Hill, Michael Virtanen and George M. Walsh in Albany contributed to this report.