WASHINGTON — A Finnish freighter drops anchor in the Persian Gulf, near Dubai. Then, it slips into the Pakistani harbor of Karachi. Later, a port call is made in Bombay, India.
At one or more of these ports in 1989, the vessel quietly unloaded 106 tons of maraging steel, a special metal used in nuclear-weapons development.
Western officials know that 100 tons, sold by an Austrian manufacturer to a private European dealer, ended up in Iraq's now-defunct atomic-weapons program. Where the other six tons went remains a mystery, but some experts believe they are in Iran.
The shipment is one tiny piece in a mosaic of intelligence reports that has convinced the US, its allies, and most independent experts that Iran's Islamic regime is pursuing a ''crash program,''
as Secretary of State Warren Christopher describes it, to develop nuclear weapons.
Iran ''is at the early stages of a weapons- development program, but we believe they are keeping their options open and looking at multiple routes,'' Ellen Laipson, director of Near East and South Asian affairs for the National Security Council, told a Middle East Policy Council seminar in Washington last week.
Says another US official: ''We've seen a pattern of procurement attempts on the part of Iran to obtain nuclear equipment and technology that is not consistent with ... its civilian power program.''
US officials have been voicing similar concerns for several years, with the CIA estimating in 1993 that Iran was eight to 10 years away from making an atomic bomb. But never before have the alarms been rung so loudly than by the Clinton administration, which has embarked on a high-profile campaign to isolate Iran politically, militarily, and economically.
Iran vehemently denies seeking atomic weapons, pointing to its support for a Middle East nuclear-free zone and the recently renewed Nuclear Non-Proliferation Treaty (NPT). But US officials and independent experts believe Iran seeks nuclear weapons for several reasons, including the belief that Israel has them. Another reason, they say, is Tehran's desire to assert itself as a regional power and as resurgent Islam's leading voice.
No more Desert Storms
Zalmay Khalilzad, a former Defense Department official and Iran expert at the Rand Corporation, a think-tank, says Iran's alleged nuclear effort may also have been impelled by a realization after the 1991 Gulf war that it could never match the US in conventional arms. Iran believes ''that to confront the US, given what happened in Desert Storm, it needs to have nuclear weapons,'' Dr. Khalilzad says.
US officials and independent experts say there are no signs that Iran has made new headway against the numerous obstacles preventing its purported program from moving beyond a rudimentary stage, including a severe economic crisis. This admission has prompted critics to charge that President Clinton is using Iran for political gain: to counter his image as a weak foreign policymaker and to stop congressional Republicans from exploiting the issue themselves.
Some experts also dispute the coercive measures, such as Clinton's new ban on US firms doing business with Iran. They say that instead of weakening the Islamic regime, the US is fueling its resolve and fomenting anti-US sentiments among moderate Iranians. These experts argue for tough, but low-key diplomacy.
Still, there is near-universal agreement among experts on the need for immediate measures to derail Iran's suspected nuclear ambitions, including US pressure on Russia and China to cancel lucrative agreements to sell Iran nuclear reactors for electricity production.
''No country that seriously set out to design a nuclear weapon has ever failed,'' notes Anthony Cordesman, an Iran specialist at Washington's Center for Strategic and International Affairs. ''Given Iran's level of sophistication, they unquestionably have the technical capability. The question is how many resources they are really putting into it.''
The administration, however, faces problems in galvanizing international support for its campaign. This was underscored by Clinton's failure last month to persuade Russian President Boris Yeltsin to cancel Russia's reactor deal with Iran. Perhaps the biggest problem for the US is its own admission that it lacks irrefutable proof that Iran is pursuing anything other than a peaceful nuclear program. Unlike Iraq and North Korea, the US cannot cite a single location where Iran is conducting nuclear-arms research.
''There is no smoking gun. There is no hidden facility that we can identify,'' concedes an Arms Control and Disarmament Agency (ACDA) official who spoke on condition of anonymity.
The US position is further weakened by special International Atomic Energy Agency visits to Iran in 1992 and 1993 that failed to detect any sign of a nuclear-weapons program. The IAEA seals of approval have strengthened Russia and China in their refusals to terminate their deals to sell power reactors to the Islamic republic.
So what has led US officials and experts to the firm belief that Iran wants an atomic bomb? While loath to reveal classified information, they say scads of circumstantial evidence and US, Israeli and European intelligence reports leave no doubt that Iran is exploring a variety of approaches to acquiring nuclear weapons.
One avenue, they say, is Tehran's revival of the late Shah Muhammad Reza Pahlavi's ambitious, multibillion dollar plan to build nuclear reactors for electricity. This decision has provoked deep suspicions, because Iran has a serious shortage of hard cash, huge petroleum reserves and the world's second-largest reserves of natural gas.
''Gas would allow them to generate the same amount of energy as nuclear power at one-fifth the cost,'' observes Dr. Cordesman.
While power reactors would conform to the NPT, US officials and independent experts say Iran could use them as fronts through which to import restricted ''dual use'' technologies that have nuclear-weapons applications. This concern lies at the heart of the US objections to the proposed Russian and Chinese reactor sales.
''It gets you a long way toward a weapons program without violating anything,'' Khalilzad says. Echoing another official US concern, he says power reactors would also provide Iranian technicians with experience in handling nuclear materials.
US officials say another route Iran is exploring is the black-market purchase in the former Soviet Union or elsewhere of weapons-grade uranium or even a complete nuclear device.
''Based on a wide variety of data, we know that since the mid-1980s, Iran has had an organized structure dedicated to acquiring and developing nuclear weapons,'' Mr. Christopher says. Among other things, he says Iranian agents tried in vain in 1992 to buy ''substantial quantities'' of enriched uranium from a plant in Kazakhstan.
US officials and experts say Iran is also trying to acquire the technology to transform natural uranium into weapons-grade material.
The process, known as enrichment, involves separating out the uranium isotope -- U-235 -- used in nuclear weapons. This is done with networks of advanced centrifuges that rotate at six times the speed of sound. The devices are made of maraging steel, the cargo carried by the Finnish freighter in 1989.
US officials and independent experts say Iran has used front companies in Europe and elsewhere in attempts to buy restricted technologies needed for designing and manufacturing centrifuges, such as balancing machines and diagnostic equipment. Iraq and Pakistan used this same method to build their nuclear-weapons programs, they say. Khalilzad says it ''is possible'' Pakistan may even have given Iran a list of the companies it used and, more alarming, a centrifuge design.
In pursuit of this effort, US officials say Iran is trying to lure home with lucrative job offers Western-trained expatriate Iranian physicists and other scientists.
Iran has used university research programs as cover to obtain dual-use technologies as well, US officials and experts say.