General Jones told his counterpart, Sergei Prikhodko, that the United States was going to go public with the intelligence. Meanwhile, in the hallways of the United Nations and over the phone, American and European officials debated when, and how, to present their case against Iran to the world.

European officials urged speed, saying that Mr. Obama should accuse Iran of developing the secret facility first thing Thursday morning, when he presided over the Security Council for the very first time. It would have been a stirring and confrontational moment. But White House officials countered that it was too soon; they would not have time to brief allies and the nuclear watchdog, the International Atomic Energy Agency, and Mr. Obama did not want to dilute the nuclear nonproliferation resolution he was pushing through the Security Council by diverting to Iran.

In the end, Mr. Obama stood on the floor of the Pittsburgh Convention Center on Friday morning, flanked by President Nicolas Sarkozy of France and Prime Minister Gordon Brown of Britain, and called the Iranian facility “a direct challenge to the basic foundation of the nonproliferation regime.”

Added Mr. Brown, “The international community has no choice today but to draw a line in the sand.”

This account of the days leading up to the announcement on Friday is based on interviews with administration officials and American allies, all of whom want the story known to help support their case against Iran.

The Iranians have continued to assert that their nuclear program has peaceful intentions. And while American officials say the secretive nature of the program lends support to the view that it is truly an expanding weapons program, even United States intelligence officials acknowledge that there is no evidence that Iran has taken the final steps toward creating a bomb.

There was “a fair amount at anger” within the administration over Iran’s disclosure, a senior administration official said. But there was also some satisfaction. A second senior official said: “Everybody’s been asking, ‘Where’s our leverage?’ Well, now we just got that leverage.”

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Administration officials said that Mr. Obama had two goals in going public: to directly confront Iran with the evidence, and to persuade wavering nations to take a hard line on Iran.

In fact, the makings of the administration’s strategy was hatched months before, when the White House first came to believe that the complex, built into a mountain on property near Qum controlled by Iran’s powerful Revolutionary Guards, might be a part of the nuclear program. Over time, the file that intelligence officials accumulated on the facility developed as a cudgel, a way to win over wary allies and test if the Iranians were being truthful in their disclosures.

Senior intelligence officials said Friday that several years ago American intelligence agencies under the administration of George W. Bush discovered the suspicious site. The site was one of Iran’s most closely guarded secrets, the officials said, known only by senior members of Iran’s nuclear establishment. The officials said that housing the complex on the base gave it an extra layer of security.

Mr. Obama was first told about the existence of the covert site during his transition period in late 2008, White House officials said, after he had been elected but before he was inaugurated. But it was not until earlier this year that American spy agencies detected the movement of sensitive equipment into the facility — a sign, they believed, that whatever work was involved was nearing its final stages.

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American officials said Friday that the facility could have been fully operational by next year, with up to 3,000 centrifuges capable of producing one weapon’s worth of highly enriched nuclear material per year.

“Over the course of early this year, the intelligence community and our liaison partners became increasingly confident that the site was indeed a uranium enrichment facility,” a senior administration official said. He said that Mr. Obama received regular intelligence updates on the progress of the site.

The officials said that they developed a detailed picture about work on the facility from multiple human intelligence sources, as well as satellite imagery. A senior official said that intelligence was regularly shared among American, British and French spy agencies, and that Israeli officials were told about the complex years ago. They were not more specific about when they first learned about it.

At some point in late spring, American officials became aware that Iranian operatives had learned that the site was being monitored, the officials said.

As the administration reviewed its Iran policy in April, Mr. Obama told aides at one point that if the United States entered into talks with Iran, he wanted to make sure “all the facts were on the table early, including information on this site — so that negotiations would be meaningful and transparent,” a senior administration official said.

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As the summer progressed, British, French and American officials grew more worried about what Iran might do now that it was aware that security at the complex had been breached.

In late July, after the mass protests over Iran’s disputed election had died down, Mr. Obama told his national security team to have American intelligence officials work with their British and French counterparts to secretly put together a detailed presentation on the complex.

“That brief would be deployed in the case of a number of contingencies,” the administration official said. “If Iran refused to negotiate, in the case of a leak of the information, and even an Iranian disclosure.” Mr. Obama asked his aides to have the presentation ready by the General Assembly meeting.

“We could not have negotiations of any meaning if we were only going to talk about overt sites and not covert sites,” a senior administration official said.

As late as last weekend, American officials were still uncertain about when to publicly present the intelligence about the secret enrichment facility. The game plan changed Tuesday, when officials from the nuclear watchdog agency informed the Americans that Iran had sent the letter describing the “pilot” facility.

At his meeting at the Waldorf the next morning, Mr. Obama decided that he would personally tell Mr. Medvedev, the Russian president, when they met Wednesday afternoon for a previously scheduled meeting. Mr. Obama also spoke with Mr. Sarkozy and Mr. Brown. Meanwhile, Jeff Bader, a senior White House adviser for China, informed his Chinese counterparts.

On Thursday, while Mr. Obama was leading the Security Council meeting, General Jones left his seat behind Mr. Obama, walked over to Mr. Prikhodko, the Russian national security adviser, and whispered in his ear. Mr. Prikhodko got up and followed General Jones out of the room. Minutes later, General Jones sent an aide back to get his Chinese counterpart as well.

Administration officials said they were gratified with Russia’s reaction — Mr. Medvedev signaled he would be amenable to tougher sanctions on Iran. The Chinese, one administration official said, were more skeptical, and said they wanted to look at the intelligence, and to see what international inspectors said when they investigated.

The lessons of the Iraq war still lingered.

“They don’t want to buy a pig in a poke,” the senior administration official said.