The U.S. claims led Tehran's ambassador to Iraq, Hassan Kazemi-Qomi, to challenge American officials last month to show "any shred of evidence" of Iranian meddling.
The U.S. ambassador, Zalmay Khalilzad, promised last week to do so, and American officials initially planned to release their dossier Tuesday.
But the release was delayed, and Sean McCormack, the chief State Department spokesman, declined Wednesday to predict when the report would be issued.
"We'll do this on our own timeline," he told reporters. "And we're going to do it in such a way that it is properly presented, it is clear, and that it is done in such a way that ... we don't in any way jeopardize [U.S. officials'] ability to further collect information about these networks."
This week, McCormack denied that U.S. intelligence failures and erroneous pre-Iraq war claims had made the job of preparing the new dossier more difficult.
The administration's quandary is one more indication of the difficulties the United States faces in Iraq as it tries to limit the influence of the Iranians, whom it increasingly views as its chief regional rival. There are thousands of Iranians in Iraq. Some of them have strong ties to the U.S.-backed government.
One former senior U.S. defense official said that preparing such a case would involve trying to cull sensitive data for presentation to a skeptical American public.
"It's a losing proposition for the administration," said the former official, who declined to be identified when addressing intelligence issues.
U.S. military and embassy officials in Baghdad have been trying to build a case with a variety of evidence, according to officials.
But officials involved in interagency meetings on the issue in Washington, including some in the State Department and intelligence agencies, believe that some of the material overstates murky evidence and casts a negative light on Iranians who may not be guilty.
Another difficulty is that if some of the most sensitive information is withdrawn to protect intelligence sources, the result could be a weak and unconvincing report, the officials said.
The American official who requested anonymity said that although there were differences over the evidence, there was wide agreement within the U.S. government that Iran's actions were a threat and that the United States, while avoiding war, should be more aggressive in confronting Iran in Iraq.
