The United States Monday made public a report by U.S. and British experts accusing Ukraine's government of failing to fully cooperate in an investigation of whether Ukraine has sold Iraq a sophisticated radar system, in violation of U.N. sanctions. The affair has chilled relations between the Bush administration and the government of President Leonid Kuchma in Kiev.

U.S. spokesmen had already made clear the Bush administration's displeasure over the Kuchma government's handling of the affair.

But the 16-page report, made available to reporters here, explains U.S. concerns in detail. It says the Ukrainian side failed to produce evidence backing up its denial of illegal arms dealings with Iraq, and that there are "serious concerns about the credibility" of Ukraine's own investigations of the matter.

The controversy burst into the open in September, when U.S. officials said they had confirmed the authenticity of an audiotape provided by a former Ukrainian presidential security guard in which President Kuchma is overheard approving the sale of the advanced "Kolchuga" radar system to Iraq.

Such a transfer would violate U-N sanctions and be of deep concern to the United States and Britain, since the "Kolchuga," a hard-to-detect "passive" radar would greatly increase the threat to U.S. and British aircrews enforcing the "no-fly-zones" over Iraq.

The Kuchma government claims the tape, allegedly of a conversation between Mr. Kuchma and a senior aide in July of 2000, was doctored and it denies any radar transfer took place.

The U.S. and British experts were invited in to look into the matter first-hand. But their report says Ukrainian officials gave "evasive responses" to direct questions about whether the alleged $100-million sale was consummated, either directly or through a third party, and it says the possibility that Iraq now has the radar "must remain open."

It further raises questions about Ukraine's accounting for the "Kolchugas" produced over the years, and it faults the country's export-control process, which it says does not provide adequate safeguards against senior officials misusing or bypassing the system altogether.

The report will do nothing to arrest the deterioration of relations between the Kuchma government and the Bush administration, which has already suspended a $55-million annual aid program to Ukraine as an initial step in a policy review.

The chill was evident at last week's NATO summit in Prague, where President Kuchma attended a meeting of the alliance's Euro-Atlantic Partnership Council despite the fact he was not invited, and was pointedly shunned by other leaders.