WASHINGTON, May 31 After 27 years in which the United States has refused substantive talks with Iran, President Bush reversed course on Wednesday because it was made clear to him by his allies, by the Russians, by the Chinese, and eventually by some of his advisers that he no longer had a choice.
During the past month, according to European officials and some current and former members of the Bush administration, it became obvious to Mr. Bush that he could not hope to hold together a fractious coalition of nations to enforce sanctions or consider military strikes on Iranian nuclear sites unless he first showed a willingness to engage Iran's leadership directly over its nuclear program and exhaust every nonmilitary option.
Few of his aides expect that Iran's leaders will meet Mr. Bush's main condition: that Iran first re-suspend all of its nuclear activities, including shutting down every centrifuge that could add to its small stockpile of enriched uranium. Administration officials characterized their offer as a test of whether the Iranians want engagement with the West more than they want the option to build a nuclear bomb some day.
And while the Europeans and the Japanese said they were elated by Mr. Bush's turnaround, some participants in the drawn-out nuclear drama questioned whether this was an offer intended to fail, devised to show the extent of Iran's intransigence.
Either way, after five years of behind-the-scenes battling within the administration, Mr. Bush finally came to a crossroads at which both sides in the debate over Iran engagers and isolaters, and some with a foot in each camp saw an advantage in, as one senior aide said, "seeing if they are serious."
Mr. Bush, according to one participant in those debates, told Secretary of State Condoleezza Rice several months ago that he needed "a third option," a way to get beyond either a nuclear Iran or an American military action.
Ms. Rice spent a long weekend in early May drafting a proposal that included a timetable for diplomatic choreography through the summer.
"Nobody wants to get to that kind of crisis situation whether it is us or the next administration where you either accept an Iranian weapon or you are forced to do something drastic," said the participant, who declined to speak on the record about internal White House deliberations.
The idea of engagement is hardly new. When Colin L. Powell was secretary of state, several members of his senior staff argued vociferously that the United States needed to test Iran's willingness to deal with the United States especially in the aftermath of Sept. 11.
There was strong opposition from the White House, particularly from Vice President Dick Cheney, according to several former officials.
"Cheney was dead set against it," said one former official who sat in many of those meetings. "At its heart, this was an argument about whether you could isolate the Iranians enough to force some kind of regime change." But three officials who were involved in the most recent iteration of that debate said Mr. Cheney and others stepped aside perhaps because they read Mr. Bush's body language, or perhaps because they believed Iran would scuttle the effort by insisting that the Nuclear Nonproliferation Treaty gives it the right to develop nuclear fuel. The United States insists that Iran gave up that right by deceiving inspectors for 18 years.
In the end, said one former official who has kept close tabs on the debate, "it came down to convincing Cheney and others that if we are going to confront Iran, we first have to check off the box" of trying talks.
Mr. Bush offered a more positive-sounding account: "I thought it was important for the United States to take the lead, along with our partners, and that's what you're seeing. You're seeing robust diplomacy."
As part of the diplomatic timetable, Ms. Rice will be in Vienna on Thursday to endorse an international offer to Iran that includes several plums. Among them will be the dialogue with Washington that Iran has periodically sought, a lifting of many long-standing economic sanctions, and even light water reactors for nuclear power with Russia and the West controlling access to the fuel.
Yet skepticism abounds. "It's true that the conditions are significantly different than they were four or five years ago, but candidly they are not as favorable now for the United States," said Richard Haass, who as the head of the State Department's policy planning operation during Mr. Bush's first term was a major advocate of engagement with Iran.
First, the new president, Mahmoud Ahmadinijad, "has vowed that the country will never back down on enriching uranium.
"Oil's at $70 a barrel instead of $20, said Mr. Haass, now the president of the Council on Foreign Relations. "And we are bogged down in Iraq," where the United States is vulnerable to Iranian efforts to worsen the violence and arm the insurgents.
But the internal debates in the White House included vigorous discussion of the risks associated with any effort to negotiate with foes suspected of seeking nuclear weapons. And in this, Mr. Bush already has bitter experience.
In its dealings with North Korea, which Mr. Bush branded a member of the "axis of evil" along with Iran and Iraq, the administration also decided a few years ago to try limited engagement, locked arm-in-arm with neighboring nations.
But North Korea has kept making weapons fuel, and the allies have not stayed united: China and South Korea continue to aid the North. The Iranians have doubtless noticed.
The question now is whether there is any middle ground between Mr. Bush's demand that Iran give up everything, and Iran's insistence that it will give up nothing. Without breaking that logjam, the American-Iranian dialogue may never begin.