“They never come up with actual facts; they never come up with actual cases,” Ms. Bolkovac said.

She won a wrongful dismissal case in 2003 against a subsidiary of Virginia-based DynCorp International, which was contracted by the State Department to provide police officers for the United Nations peacekeeping force in Bosnia. But Ms. Bolkovac says she has never been hired by another peacekeeping mission. (DynCorp issued a statement noting that “The Whistleblower” was a work of fiction and that new owners had since enacted their own zero tolerance policy.)

United Nations officials brandish the statistics published on the organization’s peacekeeping Web site as evidence of transparency. The numbers, whose source is somewhat vague, indicate that cases dropped from 108 substantiated accusations of sexual exploitation and abuse in 2007 to 85 in 2008, then to 63 in 2009, 33 last year and just 5 so far in 2011.

But more than 200 such accusations remain unresolved, and the United Nations annual report on such crimes for 2010 noted that sexual activity with minors and nonconsensual sex represented more than half of reported accusations, little changed since 2008. Cases have come to light where peacekeepers paid children $1 or with candy to make a rape seem like prostitution.

Finally, efforts to gather information from troop contributors about legal or disciplinary action are often ignored. The United Nations got answers roughly a quarter of the time, or 88 responses from 333 queries sent, since 2007, according to its figures.

Senior officials defend the numbers as improving, and argue that publicly shaming member states would make finding peacekeeping troops more difficult. “Going into a blame and shame approach is counterproductive because this requires a mind-set change,” said Susanna Malcorra, head of the logistics end of peacekeeping.

Activists and some diplomats condemn the United Nations as timid, with internal policing particularly weak under Secretary General Ban Ki-moon. Mr. Ban waged an extended feud over hiring with the head of internal oversight before she left in 2010, leaving dozens of investigator jobs empty. Senior officials admit that its investigators have the mandate to do more to track sexual abuse cases.