He was a former undercover police officer with a bodybuilder’s physique and a knack for charming people in high places such as Rudy Giuliani and even President Bush. But since his meteoric rise, Bernard Kerik has turned radioactive.

In the past three years, a string of revelations about Kerik’s personal and professional improprieties have embarrassed his supporters and fueled criminal prosecutions _ including an investigation that could result in an indictment on tax evasion and corruption charges.

Federal prosecutors and Kerik’s attorney, Kenneth Breen, declined to comment Thursday on secret grand jury proceedings in White Plains, N.Y., where the former police commissioner could be arraigned Friday if an indictment is handed up.

Authorities have alleged that Kerik took tens of thousands of dollars in services from benefactors and never reported it as income. Earlier this year, he rejected a plea deal, and his attorney insisted he had done nothing wrong.

An indictment would be the latest chapter of a downfall that began within days of Kerik’s nomination in 2004 to head the Department of Homeland Security. At the time, he was billed by the former mayor as a no-nonsense, self-made lawman who helped restore calm following the Sept. 11 terrorist attacks.

But the nomination was confronted with news reports about stock-option windfalls, his connections with people suspected of doing business with the mob and overlapping extramarital affairs with two women: Judith Regan, the publisher of his memoir, and a city correction officer. The liaisons reportedly occurred in an apartment near ground zero that had been set aside for rescue workers.

Kerik, 51, who married his current wife in 1998 and has two children with her, apparently became close with Regan while writing “The Lost Son,” in which he described being abandoned by his prostitute mother.

Kerik rose from cop to Giuliani’s correction commissioner in the late 1990s. From there, he became police commissioner and later went to work in Iraq rebuilding the country’s police force.

But his past troubles never seemed far behind. Kerik had committed to work as a national security adviser in Guyana and Trinidad, but had to pull out. The president of Guyana said he did not want either country “tainted” by the corruption allegations in the U.S.

And then there was the failed Homeland Security nomination. Democrats who opposed the nomination focused on Kerik’s recent windfall from exercising stock options in a stun-gun company that did business with the department. His take: $6.2 million.

Kerik sought to spare the White House and Giuliani further shame by withdrawing his name. But by then, state investigators were already aware of the expensive renovations done to his Bronx apartment in 1999, including built-in cabinets and a rotunda with a marble entryway. They alleged the work was paid for by Mafia-connected builders who sought his help winning city contracts.

Giuliani was forced to testify before a state grand jury in a case that resulted in Kerik pleading guilty last year to accepting illegal gifts while on the city payroll. The plea spared Kerik jail time and preserved his new career as a security consultant, but his name was quietly removed from a downtown jail named in his honor.

The state case isn’t over: Two brothers who run the construction firm have pleaded not guilty to charges they lied to the grand jury about their relationship with Kerik.

In the past 18 months, a federal grand jury took up the tax case, quizzing another parade of witnesses. They included a commercial real estate developer who picked up the $9,000-a-month tab for a luxury Upper East Side apartment that Kerik lived in around the time he left the police department in 2001.

The federal case also involved allegations that former Westchester County District Attorney Jeanine Pirro tried to recruit Kerik to eavesdrop on her husband, whom she suspected of having an affair, in 2005. But authorities have indicated that no charges would arise from the encounter.