WHEN IT comes to political hypocrites, Clinton impeachment prosecutor David P. Schippers wrote the book.

DAVID & NANCY When their affair was going hot and heavy.

Clinton's chief accuser, who pilloried the President for lying about his affair with Monica Lewinsky, has written a new book that he says exposes "lies, cowardice, hypocrisy, cynicism, amorality" in Washington.

But Schippers himself carried on his own affair with an employee nearly 20 years his junior -- as sources told The ENQUIRER in early 1999.

Schippers -- chief investigative counsel for the House Judiciary Committee -- and his law-office manager Nancy Ruggero had a 25-year affair behind the back of Schippers' wife of 45 years, say sources.

Their romance ended only when Ruggero got tired of waiting for Schippers to leave his wife and married another man several years ago, sources told The ENQUIRER. But she remained in his employ and was an aide during the impeachment proceedings. And Schippers actually brought Ruggero into a House hearing room where he passionately presented his case against Clinton!

Bitter over the politicking and deals that let Clinton remain in office, Schippers has written a book called "Sellout: The Inside Story of President Clinton's Impeachment."

Schippers paints himself as a simple, honest investigator whose search for truth and justice falls victim to cynical Washington politics. But not once does he admit to having the same private failings that got Clinton into hot water.

"Dave Schippers is a bigger hypocrite than any of the Washington bigwigs he blasts in his book," an insider told The ENQUIRER.

"First he brings his mistress to watch him prosecute the President for having a mistress. Then he writes a book about how sleazy Washington politicians are.

"Imagine the gall of the man!"