A United Nations whistle-blower who prevailed in a landmark case that exposed evidence of retribution against internal criticism, but who was awarded only a tiny fraction of his claimed financial losses, sought help from Secretary of State John Kerry on Monday, asking him to withhold 15 percent of the American government’s United Nations budget allocation.

The whistle-blower, James Wasserstrom, an American whose protracted legal battle with the United Nations ended a nearly 30-year career there, cited an American law that requires such withholding if the secretary of state determines that the United Nations is failing to protect whistle-blowers from retaliation.

The case has become a potential source of acute embarrassment to Secretary General Ban Ki-moon because it has cast an unflattering light on internal protections, put in place more than six years ago, that were theoretically devised to shield whistle-blowers, but in practice appear to discourage them.

Even though he won his case, Mr. Wasserstrom said a United Nations oversight panel judge’s decision last month to award him only $65,000 of his claimed $3.2 million in total damages had sent a message that “clearly tells U.N. staff that even when a whistle-blower wins, he loses.”

The coercive pressure of the withholding threat, Mr. Wasserstrom said in a letter to Mr. Kerry, could force changes in what Mr. Wasserstrom described as an organizational culture in which “U.N. personnel who are aware of misconduct, corruption and fraud are likely to remain silent.”

The United States is the largest single contributor to the regular budget of the United Nations among its 193 members, accounting for 22 percent of the total. The 2012-13 regular budget is about $5.4 billion.

Mr. Wasserstrom, who is now an anticorruption adviser at the United States Embassy in Kabul, Afghanistan, released the text of the letter at a New York news conference arranged with the help of the Government Accountability Project, a nonprofit group that advocates for whistle-blowers. Copies of the letter also were sent to American officials, including Ambassador Susan E. Rice and more than two dozen members of Congress who sit on committees that have a say about budget allocations to the United Nations.

Mr. Kerry was traveling in the Middle East, and it was unclear whether he had read the letter. But a State Department official, referring to the law cited by Mr. Wasserstrom, Section 7049(a) of the 2012 Consolidated Appropriations Act (H.R. 2055), said Mr. Wasserstrom’s assertion did not reflect the department’s position.

“We do not believe any withholdings are required pursuant to Sec. 7049(a) at this time,” said the official, who spoke about Mr. Wasserstrom’s case, which is still pending, on the condition of anonymity. The official also said the United States had been pressing Mr. Ban “to expedite the development of strengthened protections against whistle-blower retaliation.”

A spokesman for Mr. Ban at the United Nations, Eduardo del Buey, said he could not comment because the dispute was still under litigation.

Shelley Walden, the international program officer of the Government Accountability Project, who appeared with Mr. Wasserstrom at the news conference, told reporters that after his prolonged legal brawl, “Mr. Wasserstrom is far worse off financially than if he had simply remained silent.”

Mr. Wasserstrom’s case dates to 2007, when he was the top anticorruption officer at a United Nations mission in Kosovo and reported signs of misconduct among other United Nations officials there to his superiors.

A few months later, his office was closed, his post was abolished and an internal United Nations inquiry into his own behavior was ordered that included searches of his home and car and seizure of his property. Mr. Wasserstrom said he had been treated like a criminal.

A review under the United Nations employee disciplinary judicial system concluded that he was not the victim of retaliation, and Mr. Wasserstrom was terminated in November 2008. After four years of appeals through that system, a ruling last June by a dispute tribunal found Mr. Wasserstrom had been subjected to retaliation and “wholly unacceptable treatment in breach of right to due process.”

Under the whistle-blowing program instituted in 2006, the Ethics Office had received at least 343 inquiries from whistle-blowers about protection against retaliation as of last June, according to the Government Accountability Project, but only 1 percent of them were ultimately validated as retaliation. Mr. Wasserstrom said in his letter that such a record “defies logic, probability and common sense.”