By ALAN COWELL
LONDON, Sept. 6 - A leading British research institute said today that Iran was at least five years away from producing sufficient material for "a single nuclear weapon" - but only if it chose to ignore international reaction and "throw caution to the wind."
The International Institute for Strategic Studies said its conclusions were based on a variety of public sources of information, including visits to Iranian nuclear sites arranged by the Iranian authorities.
"Nevertheless," the Institute's director, John Chipman, told reporters, "there remains a good deal that cannot be known for certain from the outside."
Dr. Chipman was presenting a report at a diplomatically delicate time. Iran angered western negotiators by resuming limited uranium conversion activities at a plant in Isfahan on Aug. 8, ending a suspension of nuclear activities agreed with the European Union last November.
On Sept. 19, moreover, the United Nations nuclear agency's board of governors is to meet to consider the next step. Iran has rejected a call by Britain, France and Germany - the European Union troika negotiating with Teheran over its nuclear ambitions - to re-suspend its nuclear activities before the Sept. 19 meeting.
Western nations, including the United States, have threatened to refer Iran to the United Nations Security Council, where it could face an array of penalties over its nuclear policies. Initially, a European official said, the intention is to seek "the backing, the weight" of the Security Council to isolate Iran internationally.
The deadlock has produced a degree of pessimism over the prospect of a negotiated settlement. Dr. Chipman said today that, compared to assessing Iran's technical capabilities, "the greater difficulty is conjuring a satisfactory diplomatic outcome to the impasse."
The United States argues that Iran is using its nuclear program to further ambitions to produce nuclear weapons, but Iran maintains the program is designed only for peaceful purposes.
In its report, the Institute of Strategic Studies suggested that Iran had two principle options to produce highly-enriched, weapons-grade uranium, one at a relatively small pilot centrifuge plant at Natanz and the other at an industrial-scale centrifuge plant in the same location whose construction would take more than a decade to complete.
"If Iran threw caution to the wind and sought a nuclear weapon capability as quickly as possible without regard for international reaction, it might be able to produce enough highly-enriched uranium for a single nuclear weapon by the end of this decade" if it overcame an array of technical difficulties, the report said. The likely timetable for Iran's nuclear development was roughly in line with European Union assessments.
By contrast, "if Teheran does not feel compelled to acquire nuclear weapons urgently or judges that the risk of breaking out with a marginal capacity is too great, it could wait until it completes the industrial-scale centrifuge plant at Natanz," the report said.
While that might take more than 10 years, it would make it easier "to pursue covert enrichment options," the report said.
It said Iran's "ability to produce weapons-grade plutonium seems more distant." The report described Iran's chemical and biological weapons as "much more difficult to assess." In a section relating to Iran's missiles, it said Iran had deployed up to 72 short- and medium-range missiles and possibly 12 intermediate- range missiles capable of striking targets in Israel, Turkey and southern Russia.
Dr. Chipman said the liquid fuel technology for the missile program had been acquired from North Korea. "As far as is known Iran's missile forces are armed with conventional high explosive warheads," he said, adding that Iran could probably build primitive chemical or biological warheads "if it chose to do so."
Describing the diplomatic calculations, Dr. Chipman said it would be important for western negotiators "to apply pressure and create inducements to persuade Iran not to develop a fuel cycle capability that it could turn later into a weapons program."
"On the other hand it will be important to apply international diplomacy in such a way that does not inspire Iran to abandon all restraint and seek a nuclear weapons capability without regard to international repercussions," he said.
A previous report by the Institute covering Iraq and published in September 2002 was taken by Prime Minister Tony Blair's government as supporting the argument that Saddam Hussein had "access to biological and chemical weapons" - the rationale for Britain's entry into the 2003 Iraq war. No such weapons have been found.
