With growing impatience over what he sees as foot-dragging by the Obama administration to explain the so-called "red line" that Iran cannot cross if it wants to avoid war, Israeli Prime Minister Benjamin Netanyahu made his case to the world for where to draw the line.

The prime minister thanked President Obama for his speech before the United Nations two days earlier in which he warned he would do what it takes to prevent Iran from going nuclear. The attempt to show solidarity with the U.S. leader belied a fundamental argument, becoming ever more public, over when military action would be required to take out the nuclear program.

Diagrams in hand during his speech to the U.N. General Assembly, Netanyahu drew an actual red line through the level at which Iran's ability to build nuclear weapons would be irreversible. By next spring or summer, he said, Iran will have enriched enough uranium to build a nuclear weapon and a "clear red line" must be drawn to make clear to Iran it must halt its uranium enrichment before then.

Netanyahu was referring to Iran's enrichment of uranium to 20% purity, a level it says is required for medical isotopes but which also brings it close to bomb-fuel grade. Iran maintains it is not trying to develop nuclear weapons and insists the uranium enrichment program is meant for peaceful purposes.

Equating the threat posed by a nuclear armed Iran to a nuclear-armed al Qaeda, Netanyahu urged the world to act.

Israeli and U.S. officials have said the two countries are in 100% agreement of the pace and scope of the development of the Iranian effort.

The debate between the United States and Israel centers on a decision by Iran to acquire a nuclear bomb versus its "breakout capacity" to do so.

Netanyahu said Thursday that Iran's enrichment program should be the barometer for the point of no return because with Iran moving much of its nuclear work underground, the enrichment facilities are the only visible nuclear installations that can be credibly targeted.

Israel worries that Iran's nuclear development will progress past a point where the Israelis can stop Iran from obtaining a nuclear weapon.

The United States, with its superior military capabilities, has greater latitude to decide how far is too far. The Obama administration has not laid out the U.S. threshold and offered a "we'll know it when we see it" explanation of the "so-called breakout move."

Actually, President Obama has laid out a red line of sorts, saying a decision by Iran to go nuclear and a move to assemble a bomb would prompt him to act. Defense Secretary Leon Panetta said last month the United States had no intelligence to indicate a decision by Iran to go after the bomb. But Netanyahu, Israeli Defense Minister Ehud Barak and others argue Iran can continue to develop the expertise and technology needed to make a bomb and gain this breakout capacity without having made an official "decision."

In this scenario, Israel's greatest fear is Iran will have all its ducks in a row and can quickly assemble a nuclear weapon after a decision is made. Panetta said once Iran has made the decision to build a bomb; the United States believes it would take Iran "about a year" to complete the required work to finish it.

Netanyahu argued that final stage could take as little as "a few months, possibly a few weeks."

But he said, "I believe that faced with a clear red line, Iran will back down."

This week Iranian President Mahmoud Ahmadenijad told reporters he did not rule out a negotiated settlement in talks with the United States, Britain, France, China, Russia and Germany.

The world powers known as the P5 plus 1 met Thursday night to discuss how to move forward on their two-track policy of seeking talks with Iran while turning up the pressure on the Iranian regime with sanctions in the face of continued nuclear antics

When a senior administration official briefed reporters after the meeting, it was clear the only progress the group could cite was that it was unified in its belief that a nuclear-armed Iran was not acceptable.

That's little comfort for Netanyahu, who soon will have to make some tough decisions as to whether the red line he so artfully drew is close to being crossed.