Blame it on Roman Polanski.

Initial prosecution concerns about Dominique Strauss-Kahn skipping bail — à la the infamous pedophile filmmaker — set in motion the hurried events that led to the international banker being indicted only four days after his arrest.

“[Strauss-Kahn’s lawyers] begged them not to indict,” said one defense source.

“Why put this into a grand jury before you have your ducks in a row?” the source said the banker’s lawyers asked. “Why commit your witnesses to testify under oath? Why do this before you even have your forensics back?”

Some six weeks later, the accuser’s credibility, and the case, have fallen apart, according to prosecution and defense sources.

But prosecutors were adamantly against taking any risk that Strauss-Kahn would abscond, as Polanski did in 1978, fleeing to France hours before being sentenced for having sex with a 13-year-old girl during a photo shoot.

France has no extradition agreement with the United States, Chief Assistant DA Daniel Alonso reminded Manhattan Criminal Court Judge Melissa Jackson in asking, successfully, for the extraordinary step that Strauss-Kahn be held without bail.

And with Strauss-Kahn incarcerated, prosecutors were bound by state statute to indict him quickly.

“It’s just like Roman Polanski,” Alonso had argued to the judge May 16. “It’s the same exact situation.”

Mayor Bloomberg yesterday defended Manhattan DA Cyrus Vance Jr. for bringing the charges quickly, noting, “He probably made the right decision, because if the allegations were true, are true, he had a legitimate worry about somebody fleeing this country. We’d never get them back.

“So he didn’t have much choice but to rush to do something.”