The man who tried unsuccessfully for almost a decade to spur federal securities regulators to investigate Bernard L. Madoff did not initially disclose his own identity to regulators because he feared for his life, according to testimony he has apparently prepared for a Congressional hearing Wednesday morning.

The witness, Harry Markopolos, will testify that Mr. Madoff “was one of the most powerful men on Wall Street and in a position to easily end our careers or worse,” and that his fund “posed great danger” to those who investigated it, based on a version of his remarks that emerged Tuesday evening.

While the testimony, posted on the Fox Business and Wall Street Journal Web sites, mirrors statements he has made on his own site and elsewhere, neither he nor his lawyers could be reached to confirm its authenticity.

Mr. Markopolos, an independent investigator who works for institutional investors, is to be questioned about his frustrated dealings with regulators by members of a House Financial Services subcommittee led by Paul E. Kanjorski, Democrat of Pennsylvania.