(Reuters) - Former New York State Assembly Speaker Sheldon Silver, one of the state's most powerful politicians for two decades, pleaded not guilty to federal corruption charges on Tuesday.

Silver, 71, who resigned as speaker after his arrest last month but remains the assemblyman for Manhattan's Lower East Side, is charged with mail fraud, wire fraud and using his office for extortion.

Silver entered his plea in U.S. District Court in Manhattan, where one of his defense attorneys, Steven Molo, said they planned to file a motion to dismiss the indictment.

The defense claims Preet Bharara, U.S. Attorney for the Southern District of New York, made several public prejudicial statements against Silver that would have tainted the grand jury weighing the case.

"These were statements where the U.S. Attorney excoriated the defendant, basically deprived him of the assumption of innocence and extolled his guilt," Molo said in court before U.S. District Judge Valerie Caproni.

Prosecutors called Molo's allegations "baseless."

Following his court appearance, Silver told reporters: "I'm confident I will be vindicated in the courtroom."

A lawyer, Silver became speaker in 1994, with considerable influence over New York state's budget and lawmaking processes.

Silver long listed the New York City law firm of Weitz & Luxenberg on financial disclosure forms as a source of income for representing its clients.

The grand jury indictment said he used that position to mask bribes and kickbacks, including more than $3 million earned for referring asbestos sufferers to the firm from a doctor whose medical research secretly received $500,000 in state funds at Silver's direction, as well as other benefits.

Silver kept secret from Weitz & Luxenberg the state funding he had organized for the doctor, according to the indictment, handed down last week.

Prosecutors say Silver also received $700,000 in kickbacks by steering real estate developers with business before the state legislature to another law firm.

(Editing by Ellen Wulfhorst, Bill Trott and Eric Walsh)