Two members of the City Council demanded yesterday to be told why a former state senator jailed in a bribery case, Guy Velella, was released after serving only three months of a one-year sentence.

Velella, a Republican of the Bronx who spent three decades in politics, was charged in a 25-count indictment of accepting at least $137,000 in bribes from contractors from 1995 to June 2000. He pleaded guilty in May to a single felony count, fourth-degree conspiracy, as part of a deal that protected his elderly father, one of several alleged coconspirators, from going to jail.

On Tuesday, the Conditional Release Board, a panel whose four members are appointed by the mayor, voted to release Velella and one of his co-conspirators after three months. Council Members David Yassky and Yvette Clark, both Brooklyn Democrats, issued a statement yesterday that criticized the board’s decision and called on Mayor Bloomberg to investigate the matter.

Mr. Bloomberg insisted yesterday that neither he nor his administration had anything to do with the board’s decision. He also stressed that he has appointed only two of the panel members and that one of them recused himself from the vote. The other two appointees, Mr. Bloomberg said, are holdovers from the Giuliani administration. “You know I never went near the trial or the incarceration of Senator Velella. I told my staff to stay far away. I never want anybody to think that we tried to influence it, “Mr. Bloomberg said.

Velella, who served his sentence on Rikers Island, is to receive an $80,000-a-year state pension.