After years of suspense and suspicion, Iran still denies it is trying to make a nuclear bomb. Analysts foresee the Iranians' success in a few years at most, but they disagree widely over a likely timetable.President-elect Obama says Iranian efforts to develop nuclear weapons are unacceptable. At a postelection news conference, Obama said, "We have to mount an international effort to prevent that from happening."Senior diplomats from the United States, Britain, China, France, Russia and Germany are meeting Thursday in Paris to discuss efforts to stop Iran's nuclear program with sanctions, but Russian and Chinese reluctance has stymied efforts for a unified stance.In dealing with Iran's nuclear ambitions, Obama faces questions that include whether to keep a US military threat on the table, whether to temper or increase economic sanctions on Tehran and whether to offer economic and diplomatic concessions to Iran, directly or indirectly, in exchange for a verifiable suspension of suspicious nuclear activity.Anthony H. Cordesman of the Center for Strategic and International Studies in Washington said in a report this month that Iran now has a technology base to make nuclear weapons, limited only by its current level of uranium enrichment."The worst case for a nuclear device is 2009, but it could well be 2011-2015 before Iran gets there," Cordesman said in an interview Tuesday. He added: "The critical issue is when Iran could have an effective nuclear-armed missile force. That could easily take two to three years longer."Israel says Iran could have enough nuclear material to make its first bomb within a year. The United States estimates that Iran is at least two years away."Estimates differ on the status of Iran's nuclear program because there are simply few hard facts," said Michael Makovsky, foreign policy director of the Bipartisan Policy Center.In a recent report, a CSIS task force headed by former Sens. Dan Coats, R-Ind., and Charles Robb, D-Va., concluded that once Iran produces 700 kilograms (1,543 pounds) of low-enriched uranium it could be capable of producing 20 kilograms (44 pounds) of highly enriched uranium, the minimum necessary for a nuclear device, in as little as 16 days. International inspectors found an Iranian stockpile of 75 kilograms (165 pounds) at the end of 2007.Iran insists its nuclear program is for peaceful purposes such as energy production.David Albright, a former UN arms inspector who heads the Washington-based Institute for Science and International Security, says Iran has improved its centrifuges at the Natanz desert enrichment plant and could be capable of making nuclear weapons in six months to two years.Explaining the varying estimates, Albright said: "We are talking about the future and can Iran succeed. Iran has taken a lot longer than one would expect to achieve success with enrichment than others would have thought possible."Also complicating forecasts, it is difficult to interpret whether Iran would want to make one weapon - which the institute assumes - or two or three, Albright said in an interview. "Some of the estimates depend on that choice," he said, and "sometimes people use worst case scenarios."Makovsky, meanwhile, said there are a number of elusive facts that contribute to the difficulty in making estimates. These include whether Natanz is Iran's only enrichment facility, how many centrifuges are functioning and how efficiently, and how much uranium already has been fed into the centrifuges.Even assumptions about how much fissile material is necessary to build a nuclear device vary. And it is not known how many kilograms of low-enriched uranium Iran has, Makovsky said.David Kay, the former head of the US weapons-hunting team in Iraq, has estimated Iran is two to five years away from being able to produce a nuclear weapon. That is, Iran is 80 percent of the way to a nuclear weapon, Kay said last month. But he estimated that the last 20 percent of development is the most difficult.Also, Kay said, Iran has worked on the program for 20 years without producing a weapon.Like all foreign policy issues, Iran's nuclear weapons program drew little attention from the presidential candidates during the campaign. The faltering economy dominated the discussion.But Iran looms as one of the most imminent and serious problems for Obama to confront.At one point during the campaign he said he supported unconditional talks with Iran's leaders. Later, he spoke without much elaboration in favor of direct diplomacy, which seems less bold.Either way, the incoming president is far more inclined than President Bush to deal directly with Iran's leaders.Iranian President Mahmoud Ahmadinejad congratulated Obama on Thursday, the first time an Iranian leader has offered good wishes to a US president-elect since the 1979 Islamic Revolution. Ahmadinejad sent a message to Obama in which he congratulated him for "attracting the majority of voters in the election."The text of the note was carried by the official IRNA news agency.Israeli foreign Minister Tzipi Livni, meanwhile, said Obama should not talk to Iran just yet. Such dialogue could project "weakness," she cautioned.___EDITOR'S NOTE - Barry Schweid has covered diplomacy for The Associated Press since 1973.