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"It's a much more ambiguous and elusive threat than the stark Iraqi threat," said Shai Feldman, who has written two new books on arms control and security in the Middle East.

For one thing, Iran, unlike Iraq, is not subject to an international inspection regime.

"Iran has not been defeated in a war," Feldman said during a stop in San Francisco earlier this month. "Iraq would have never accepted the kind of intrusive inspection regime it has accepted if it were not a condition of the cease-fire" that followed the 1991 Persian Gulf War.

What's more, he said, countries including Germany, France, Russia, China and Japan have significant economic stakes in Iran. Thus, they are reluctant to go along with pressuring the country to expose or diminish its arms supply.

"These countries are much less enthusiastic about implementing toward Iran the same kinds of measures that are implemented towards Iraq."

In Iraq's case, the need for such measures is abundantly clear.

By invading Iran in 1980, sustaining eight years of war and enormous casualties there and then two years later invading Kuwait, Saddam Hussein has proven his militancy beyond a reasonable doubt, Feldman said.

"This man has already shown an unbelievable propensity to behave in the most violent fashion. There's every reason to believe that if he only had the capability, he would do it again."

Iran's government, in contrast, has more than one face, he noted. On the one hand, new president Mohammad Khatami has shown signs of domestic moderation.

And while sectors of the government continue to pursue ballistic missile technology from Russia, "Iran's government has still not shown the same kind of propensity to conduct massive infractions of international law," he said.

Instead, he pointed out, Iran opts to support and encourage violence through such terrorist groups as Hezbollah in Lebanon and Hamas in the West Bank and Gaza.

The country, he said, is highly sensitive to the political and economic ramifications of committing aggressive acts.

"They always pursue the avenues of violence that can be less traced to them directly," he said. "This becomes even more of a problem in terms of understanding what the Iranians are all about."

Feldman, who recently completed a term as a senior research fellow at Harvard University's John F. Kennedy School of Government, cites terrorism as one of the prime areas on which the Jaffee Center, a national think tank, will focus under his tutelage.

Along those lines, he is currently trying to raise funds for a high-level study on preventing conventional and unconventional terrorism, encompassing nuclear, chemical and biological weapons.

The joint study by the Jaffee Center and the Kennedy School's Belfer Center for Science and International Affairs would employ a small research staff consisting of three former U.S. assistant secretaries of state as well as a number of top-level Israeli security experts.

The two-year study would zero in on operational questions of preventing terrorism, as well as the legal and ethical issues associated with extreme measures that might be taken to combat such violence.

"The U.S. and Israel have common concerns here," Feldman said, citing, on the American side, the desire to protect U.S. forces stationed in the region.

On the Israel side, the stake in preventing terrorism is clear. On this matter, Feldman admits he is frightened and confounded by the dramatic rise in the last few years from politically motivated to religiously motivated terrorism.

"This is a much more difficult problem; there's no question about it," he said.

Religiously motivated terrorists, who are willing to commit suicide for the promise of a better life in the next world, "are not really answerable to the kinds of inducements you can present" to their politically motivated counterparts, Feldman said.

So does Israel have any hope for preventing this particularly challenging breed of terrorism?

"The ABCs of fighting terrorism are intelligence, intelligence and intelligence," Feldman stressed.

Still, "I know what the question is, but I don't really have the answer."