Officials familiar with the evidence say it creates extraordinarily uncomfortable questions for the Iranians to answer, but does not definitively point to the construction of a weapon. Instead, it details work on individual technologies essential for designing and detonating a nuclear device, including how to turn uranium into bomb fuel, how to cast conventional explosives in a shape that can set off a nuclear blast, and how to make detonators, generate neutrons to spur a chain reaction, measure detonation waves and make nose cones for missiles.

Tommy Vietor, the spokesman for the National Security Council, said Saturday that “the United States believes that a comprehensive assessment would be invaluable for the international community in its consideration of Iran’s nuclear program and what to do about it.” Iran has declared that all of the documents suggesting work on how to create a weapon that could fit atop an Iranian missile are “fabrications” intended to justify an attack. The country has been the target of covert attacks, including the assassinations of some nuclear scientists and a computer worm that disabled some of Iran’s nuclear centrifuges.

The Obama administration, since coming to office, has never publicly presented detailed evidence to back up its claim that Iran is driving toward a weapon or creating the technology to assemble one quickly, should it need it. But it has discussed the evidence widely with allies.

In part the administration has hesitated to discuss the evidence because, after the failure to find weapons of mass destruction in Iraq in 2003, any American evidence is considered suspect. Widespread questions about the plot against the Saudis last week underscored how deep those suspicions run.

But Iran is a different kind of case. Inspectors visit regularly, measuring Iran’s output of uranium, including recent production of the material, enriched to 20 percent purity, that takes it far closer to the kind of fuel needed for a weapon. Iran said recently that it would produce more of the 20 percent enriched material than it needs for a small medical research reactor, which prompted new concerns that it is building a stockpile that could be converted to weapons use.

“They sought to hide their enrichment activity for years, and their covert facility at Qum, which the president revealed in 2009,” a top adviser to Mr. Obama, who spoke on the condition of anonymity because of the delicacy of the topic, said Friday. “They continue to enrich at 20 percent, and the rationale for doing so is demonstrably false.”

In June, the Treasury Department imposed sanctions on Tidewater Middle East, a company linked to the Revolutionary Guards that operates strategic container ports through which the Guards and the Quds Force have moved weapons, administration officials said. Last week, the Treasury levied sanctions on an Iranian carrier, Mahan Air, which officials said ferried weapons for the Quds Force.