The time frame for knowing whether Iran has crossed a so-called red line toward making a nuclear weapon could be shrinking as Iran increases its uranium enrichment capacity. (Read also: Rational or not, Iran is a real danger)
Last week's report from the International Atomic Energy Agency (IAEA) indicated Iran had significantly stepped up its enrichment operation, adding centrifuges used to process uranium at its Natanz and Fordow facilities and producing far greater quantities of 20% enriched uranium.
If Iran continues to enrich uranium to that level at the current expanded rate, nuclear experts say Iran would have enough material to further enrich to make a crude bomb, at the very least, by early next year. To do so, Iran would have to go another step and further enrich to the 90% level to make weapons-grade uranium, but analysts believe that is not a technically difficult achievement for Iran.
Government officials as well as nuclear scientists and experts agree the most difficult part of the enrichment process is getting to the 20% level. Achieving 90% enrichment would be much quicker and easier. Although one expert said it could take as little as a couple of weeks to enrich to weapons grade, several nuclear scientists said it would most likely take two to three months. The greater the quantities of lower-enriched uranium, the less time is needed to produce weapons grade.
IAEA inspectors visit Iran on an average of once every two weeks. As the time frame for making fissile material shrinks, Iran potentially could take the next step and produce weapons grade uranium during the weeks when the IAEA inspectors are not in country.
U.S. intelligence officials have said they don't believe Iran has made a decision yet to produce nuclear weapons. And Iranian officials have always maintained their nuclear program was for peaceful purposes.
Secretary of Defense Leon Panetta recently told a House committee that while Iran continuing to develop its enrichment capabilities is not a red line, the decision by Iran to develop a nuclear weapons is.
"The intelligence does not show that they've made the decision to proceed with developing a nuclear weapon. That is the red line that would concern us and that would ensure that the international community, hopefully together, would respond," Panetta said on February 16. Panetta added all options are on the table, including a military response.
But no one in the administration wants to publicly discuss what Iran would have to do to cross the red line.
Government officials and nuclear experts agree that developing fissile material - in this case, weapons-grade uranium - is the most difficult and time consuming part of the process to make a deliverable nuclear bomb. Developing an explosive mechanism and a delivery system for a nuclear weapon is less complicated. But administration officials are reluctant to publicly say that if Iran starts enriching its stockpile of enriched uranium to weapons-grade material, then Iran would have crossed the line.
At a congressional hearing two weeks ago, Director of National Intelligence James Clapper would only say that further enrichment would be "a negative indicator."
And Secretary of State Hillary Clinton told a House Foreign Affairs Committee hearing on Wednesday it was best for the administration to keep quiet on the subject of red lines.
"I think it's probably smarter for us to be pressing on the sanctions and the negotiations while we keep our objective of no nuclear capability absolutely clear instead of setting other benchmarks at this time publicly," Secretary Clinton said.
An Obama administration official who would only discuss the sensitive issue anonymously said Iran having a stockpile of 20% enriched uranium is "not necessarily" seen as a red line by the United States. However, Iran moving forward with 90% enrichment is "potentially a red line" which could trigger a further American response including a military option according to this official.
"It would be a worrisome indication of intent" by the Iranians, said the official, while at the same time acknowledging the main purpose for 90% highly enriched uranium is for nuclear weapons.
The official said "there are so many factors" that the U.S. and international community are looking at when gauging Iran's intent to produce weapons. The official didn't elaborate on what those factors might be.
But the official said there should be no doubt by the Iranians that "the development of nuclear weapons will result in Iran feeling the consequences from the U.S."
Then there is the question of the Israelis who believe Iran poses an existential threat to them. Will Israel be as patient as the U.S. appears to be?
The administration official maintained the U.S. red lines "are the same as Israel's." What is different, said the official is "the Israelis have a slightly different prism by which they view Iran's nuclear threat. They don't believe time is necessarily on their side. The U.S. believes there is more time than the Israelis believe," the official said.
The chairman of the House Intelligence Committee agreed Israel sees the problem through a different set of eyes.
On CNN's "John King, USA," U.S. Rep. Mike Rogers, R-Michigan, said Israel lives in a dangerous neighborhood and "they have a hard choice to make" in terms of whether to take a pre-emptive military strike. But Rogers also blamed the Obama administration for making public statements encouraging Israel to hold off on any military action. According to Rogers, neither Iran nor Israel believe the U.S. is serious about a military option.
"We've got to change that equation if we're going to I think have an impact on Iran backing down on its nuclear weapons program," Rogers said.
David Albright, a former nuclear weapons inspector who heads the Institute for Science and International Security, also stressed the importance of the U.S. and the rest of the international community making clear to Iran that crossing the red line has serious consequences, including the possibility of a military strike.
"If you fuzz that red line, then you lose all. You lose the deterrence that Iran currently feels against crossing that red line, and then you better get used to Iran having nuclear weapons," Albright said.
This could all come to a head in the next year or so when Iran might have enough enriched uranium to make a bomb. The key is whether Iran decides to go the final step and enrich to weapons-grade uranium.
But both Albright and retired Israeli nuclear scientist Ephraim Asculai doubt Iran would move ahead until they are in a position to have enough fissile material to make several bombs. Asculai said Iran would want "four to five weapons minimal for an arsenal."
If Iran keeps enriching to 20% at the current pace, Albright said "they're going to need most of this year to get the first (bomb) and if they increase production, maybe they'll have enough for three or four by the end of 2013." If Iran decides it actually wants to build a bomb at that point, then it would need a few months to further enrich the uranium to weapons grade, according to Albright.
To a degree, all of this is speculation. As Albright and Asculai point out, Iran has had problems with its centrifuges, and international sanctions have been a drag on Iran's ability to procure needed parts for its program.
IAEA inspectors have been thwarted by Iran in their attempts to visit all potential nuclear sites. And no one knows for sure whether Iran will even build a nuclear weapon.
It's that ambiguity that puts the international community on edge as Iran moves closer to at least the potential of having a bomb.