The United States and its five negotiating partners can't decide how far to go in trying to entice Iran and time presses as Iran continues to amass significant nuclear stockpiles and capabilities.

The Russians would like to offer sanctions relief, which is what the Iranians want. This would be in return for Iran ceasing to enrich uranium to 20 percent of the isotope U-235, which is used for peaceful purposes as Iran claims is its sole purpose but also to make atomic bombs. The 20 percent level, which the Iranians say is for a research reactor which makes medical isotopes, is more refined that what is needed for power reactor fuel and a significant step on the way to weapon-grade, or over 90 percent enriched, uranium. But the United States, Britain, France and Germany -- and many of their allies -- are not ready to dismantle their sanctions just in return for Iran stopping 20 percent enrichment. The sanctions, which were stepped up in July, are severely hurting Iran's oil sales and economy.

This block, which we can broadly call the West, wants Iran to first stop 20 percent enrichment as a confidence building measure that it does not seek nuclear weapons. Then the real work would begin in getting Iran to cut back on its large stockpile of up to 5 percent enriched uranium, which Iran claims is for power reactor fuel, but which the United States fears could be for atomic bombs. Still, the full sextet -- which includes Russia and China -- might give more if the Iranians comply with the three S's – stopping 20 percent enrichment, shipping out of the country the uranium at this level of refinement they have already made, and shutting Fordow, an almost impregnable site where most of the 20 percent enriched uranium is made.

The three S's have been a precondition, a gesture to demonstrate good intentions. Offering something more might include sanctions that are easy to lift, such as those on buying specialty metals -- but not the key oil and central bank sanctions. Said a Western diplomat: "If we ask for a bit more, we might be willing to give a bit more, but the idea is to test the Iranians waters to see if they are ready to deal."

Is this enough? The United States, the most influential of the six, simply does not feel that Iran has been negotiating seriously. So it is too soon, despite a decade of diplomacy on this issue, to offer too much, the Americans argue. Of course, there is the opposite point of view that Iran could be enticed into negotiation if it were offered sanctions relief. But Washington remains wary. For this Iran would have to concede more than just the 20 percent level U-235.

The sextet, also known as the P5+1, will probably stick with the incremental, conservative approach rather than offer Iran significant sanctions relief. The burden will be on the Iranians to show they are serious. The French are conservative, like the Americans. Britain would like something more ambitious, although not as far as Russia and China want to go. But diplomats say these differences are not a problem and that a common approach has already taken shape.

If the larger stockpile of uranium of low enriched uranium were to become part of the equation, there would have to be a tighter inspections regime, some form of cap to the amount Iran could stockpile. As diplomats see it, at the end of the day the idea is to reduce the proliferation risk and this must include the low enriched stockpile. United Nations Security Council resolutions call for suspension of all enrichment.

But there is room to maneuver. The sextet is willing to show flexibility if Iran is willing to prove it is serious. For instance, if Iran turned around in the negotiations and said they were prepared to do everything asked for regarding 20 percent enriched uranium but wanted more in return, the P5 plus 1 could bend and might begin to shift on sanctions. But that would need to be negotiated, and the official P5 plus 1 position remains that Iran must move first.

On their end the Iranians want to know what the endgame is, where the talks are heading and what they will get. The West does not want to make a formal offer at this point. But it may use a meeting to give Iran informally a sense of where the negotiations are going. Iran could be told in the equivalent of a diplomatic whisper that it would be able to keep a limited amount of enrichment which would, however, be subject to stringent and intrusive inspections. The six have not reached consensus about making such an offer. The concern is that Iran would publicize such a concession in order to discredit the UN effort to get it to suspend or limit enrichment.

Despite the risk, the P5 plus 1 should be willing to give more. The talks should move quickly to the larger stockpile of low enriched uranium. Iran will have to agree to: increased inspections, giving early notice of nuclear facilities under construction; matching what enriched uranium it produces to what it actually needs. At the current time, Iran does not need reactor fuel, for example, since its one Russian-built nuclear power plant in Bushehr uses nuclear fuel supplied by Russia.

If the Iranians don't know what the endgame is, they will not be willing to start the process of serious negotiations, and the new talks will fail. The Iranians could indeed say, OK, you've admitted we can keep some enrichment, you've effectively agreed we have a right to enrich, so what are we talking about? But giving a window to the endgame does not have to equate to giving away the negotiations. Steps would still have to be taken to get there, and the devil will be in these details. For instance, the Iranians could be told that they will not get sanctions relief until they start reducing their production of low enriched uranium. Once this production begins to be reined in, and possibly shipped out of the country, another logic will have set in, that of matching production to the actual civilian needs of the Iranian program, and this should begin to allay concerns about Iran developing nuclear weapons. It is important to put the ball in the Iranians' court, to make them an offer they can't or shouldn't refuse, in order eventually to show that they are the ones refusing negotiations. This would burnish US President Barack Obama's case that the United States gets credibility for possibly more drastic action by first exploring all peaceful possibilities.

For now, the likely outcome is that the United States and its negotiating partners will only tinker with the current offer and wait to see if Iran is ready to start the process of real negotiating. It does not augur well for success that no endgame is in sight.

Michael Adler, a scholar at the Woodrow Wilson International Center for Scholars, is writing a book on diplomacy in the Iranian nuclear crisis. Michael covered this extensively for five years while in Vienna, where he reported on the International Atomic Energy Agency.

This article first appeared on AOL Defense.