In an extraordinary step, a Nobel Prize-winning molecular biologist has moved to retract a research paper bearing his name after government investigators concluded it was based partly on faked data.

David Baltimore, president of Rockefeller University, had long defended the study, which has been the target of critics since its publication in the scientific journal Cell in 1986.But he took the unusual step of asking that the paper be withdrawn after a preliminary report by the National Institutes of Health was leaked to major news organizations Wednesday.

The report concludes that Baltimore "made assertions as to the veracity of experiments without evidence to support them," according to a government official speaking on condition of anonymity.

Baltimore was co-author of the research on the body's immune system. Questions about the paper centered on data supplied by co-author Thereza Imanishi-Kari, a Tufts University researcher.

Baltimore was awarded the Nobel in 1975 for his work in the interaction of tumor viruses and genetic material cells.