By DAVID E. SANGER and ELAINE SCIOLINO
WASHINGTON, April 29 — Iran and the United States have begun to reveal new strategies in their nuclear dispute that seem bound to escalate their confrontation, as both nations seek to turn to their advantage a highly critical report that portrays a nuclear program proceeding at full tilt, in growing secrecy.
In many ways, what has unfolded in the past three days resembles cold-war deception and brinkmanship, with some decidedly new twists for a very different nuclear age. As in the early days of the cold war, both sides have tried to write the rules on the fly, using every tool available — from American threats of sanctions to Iranian threats to cut off oil.
Iran, according to the International Atomic Energy Agency, has been successful in gradually blinding the agency's inspectors, increasingly denying them access to crucial sites and steadfastly refusing to answer questions about suspected links between Iran's civilian nuclear program and its military.
While Iran denies any clandestine effort to build a nuclear weapon, it is clearly drawing on the diplomatic playbook of a country that has done just that — North Korea. Iran has gone so far as to boast about, and perhaps exaggerate, its nuclear prowess to try to convince the West that its program is now unstoppable.
Gholamreza Aghazadeh, the chairman of Iran's Atomic Energy Organization, and other Iranian officials on Friday described their nuclear program as "irreversible." They argue that the United States should simply accept this — much as it now accepts that Pakistan and India will never give up nuclear technology.
Mahmoud Ahmadinejad, Iran's fiery president, said Saturday that giving up enrichment "is our red line, and we will never cross it," according to state television.
In Washington, senior Bush administration officials have taken a position at the opposite extreme. In the words of Robert Joseph, the State Department's top proliferation official, the administration is determined to ensure that "not one centrifuge spins" in Iran.
In interviews in the past two days, the officials have described a plan to turn the United Nations Security Council's "requests" that Iran cease enriching uranium into an enforceable requirement.
What has chilled the Chinese, the Russians and some others in Europe, however, is that the administration is insisting on citing Iran under Chapter VII of the United Nations Charter, which authorizes the use of penalties, and if that is inadequate, of military force.
This is still not a contest between nuclear powers — Iran is not believed to have a bomb yet, and intelligence estimates say that day is still 5 to 10 years away, assuming there is no clandestine effort that no one has detected.
Instead, it is an effort by the United States and some other nations to refashion the nuclear rules.
They want to declare that even if Iran is legally entitled under the Nuclear Nonproliferation Treaty to enrich uranium for civilian purposes, Mr. Ahmadinejad cannot be trusted to do so. By deceiving the nuclear agency about its activities, President Bush and British, French and German officials say, Iran has given up whatever treaty rights it once enjoyed.
Mr. Bush has also acknowledged that America's credibility has been deeply harmed by the intelligence failures over Iraq.
On Friday, he tried to allay concerns that he was proceeding down the same path he used to give a legal basis for the invasion he ordered 37 months ago. "There's a difference between the two countries," he told reporters, even as his European allies worry about similarities in the American strategy.
For the first time, the administration has publicly declared, as it did in the case of Iraq, that if the Security Council fails to act, Mr. Bush will organize "like-minded nations" to begin to impose punishment.
"We have not conceded the point and we will not concede the point that Iran will become a nuclear weapons power," said R. Nicholas Burns, who directs the diplomatic talks for Secretary of State Condoleezza Rice.
He insisted that Iran was mistaken if it thought that the Bush administration would ever allow its nuclear activity to go ahead— which is essentially what has happened in North Korea for the past three years, while negotiations have dragged on to the brink of collapse.
"The difference in the two situations is that in Iran you have a state situated in the most volatile area of the world, where they are the leading central banker of terrorist actions," Mr. Burns said. "What they can't count on is a compliant and divided international community."
The strategies have only hardened the other side's position.
Washington's episodic saber-rattling — from the president's vague comments that "all options" are on the table if diplomacy fails, and the increasingly public discussion of whether he or the Israelis will ultimately opt for a military strike — has so far failed.
The Iranians have responded with threats of their own, knowing that even the specter of confrontation rattles the oil markets and sends prices to new levels, enriching Iran and heightening the pain for Mr. Bush and American consumers.
The Iranians may have also overplayed their hand.
While they insist that their current activities are within their treaty obligations, they ignore the I.A.E.A.'s finding that Tehran hid some of its activities for two decades. And Friday's report accuses Iran of continuing to hide vital information.
But this dispute is about more than transparency. It is also about national pride and Iran's insistence on self-sufficiency and independence. That may help explain why Iran has celebrated enrichment with dancers in traditional dress, who paraded on national television while holding a small box said to contain the fruits of their atomic labors.
The inspectors' report confirmed that Iran had succeeded in enriching uranium at a low level, but it would take significantly more processing, equipment, and problem-solving to produce fuel for a bomb. Fabricating a warhead would take even more time, and risk detection.
"The real fight here is not over whether they have a weapons program, it is over whether they can create a nuclear weapons option," said Gary Samore, who led nonproliferation efforts in the Clinton administration and continues to study the Iranian program, speaking earlier this year.
"And that is the smoke-and-mirrors game, convincing everyone that they have that capability."
That is what most concerns senior officials inside the Bush administration. Officials who deal with nuclear strategy note that it is now widely assumed that North Korea has several to 10 nuclear weapons — even though the North Koreans have never conducted a nuclear test.
"We think the Iranians looked at the Koreans and learned a lesson," said a senior official, who would not speak for attribution on a matter of nuclear strategy.
It would be a very different approach than the one taken by the Russians in the late 1940's, or the Chinese in the early 1960's, or the Indians and Pakistanis in the late 1990's, all of whom set off nuclear explosions to prove their powers. Given the limited access allowed I.A.E.A.
inspectors, officials here and in Vienna say, there would be no way to verify, or disprove, Iran's claims.
Mr. Bush has therefore taken the position that Iran must give up everything. He said Friday, "The Iranians should not have a nuclear weapon, the capacity to make a nuclear weapon, or the knowledge as to how to make a nuclear weapon."
The Russians and Chinese view that as unrealistic; a senior Russian official said it was time for a "détente" with Iran, drawing another term from the cold war.
In Vienna, Mohamed ElBaradei, the director general of the atomic agency, has made it clear in conversations with diplomats that he believes pragmatism will eventually dictate that Iran be allowed some limited form of enrichment, monitored constantly by his agency.
But there is the fear — here, and in Vienna — that the I.A.E.A. is seeing only part of the program, and that the evasive answers to its questions hide a clandestine effort, somewhere under the desert. As Tehran restricts international inspections, it will be harder to know whether its program more closely resembles the very real one in Pakistan, whose scientists sold technology to Iran, or the nuclear mirage in Iraq.
U.S. Rejects Offer on Inspections
TEHRAN, April 29 (AP) — Iran said Saturday that it would allow United Nations inspectors to resume inspections of its nuclear facilities, but only if the dispute was returned to the United Nations' nuclear monitor.
The White House rejected the offer.
Iran gave no ground on the United Nations Security Council's demand that it stop enriching uranium but offered to allow the inspections if the Council dropped the matter; Council members have been at odds over imposing sanctions on Iran.
David E. Sanger reported from Washington for this article, and Elaine Sciolino from Vienna.
TEHRAN, April 25 — 
