Independent Counsel contacting potential witnesses in final phase of Lewinsky investigation

WASHINGTON (CNN) -- Independent Counsel Robert Ray is stepping up his ongoing investigation into whether to bring criminal charges against President Clinton for allegedly lying about his relationship with former White House intern Monica Lewinsky, CNN has learned.

Independent Counsel Robert Ray

Informed sources tell CNN's Judy Woodruff that Ray's office has started contacting potential witnesses to appear before a sitting grand jury. Sources say any witness list would certainly include Lewinsky herself.

Lewinsky's attorneys were not available for comment Friday. Ray's deputy, Keith Ausbrook, said the Office of the Independent Counsel is taking all the normal steps in an investigation of this sort, with an eye toward resolving the matter shortly after the president leaves office.

Ray has said that a decision whether to prosecute Clinton for his conduct in the Lewinsky scandal would come "very shortly" after the president leaves office. The legal questions are whether Clinton committed perjury or obstructed justice when he denied having an affair with Lewinsky in sworn testimony in the Paula Jones case.

Clinton was impeached by the House of Representatives and acquitted by the Senate, which fell 12 votes short of convicting him on a perjury charge and 17 votes short of conviction on a charge of obstructing justice.