For many months now, U.S. and European intelligence agencies have been trading theories about a spare, two-page document written in Persian that, if genuine, would strongly suggest that scientists in Iran were planning some of the final experiments needed to perfect an atom bomb.

But like so many pieces of evidence in the West's confrontation with Tehran, the neatly written memorandum, laying out the next steps of a complex scientific process, raises as many questions as it answers.

Intelligence officials say they have yet to authenticate the document, which describes research Iran would need to conduct on an advanced technology to detonate a nuclear weapon, if it was to develop one. Even if the paper is genuine, they say, it is unclear if it provides new insights into the state of Iran's weapons research.

Diplomats raised the possibility that the publication of the memo on The Times of London Web site late Sunday could be part of an effort to raise international alarm over Iran's intentions or progress in developing nuclear weapons capacity.

The Iranians have said nothing about it, or any other materials that international nuclear inspectors confront them with that suggest they have pursued - and may still be pursuing - work on a bomb design. Their silence, punctuated only by periodic responses that the evidence consists of “;fabrications”; by the CIA and others, explains why Mohamed ElBaradei, the just-departed head of the United Nations' nuclear inspection agency, declared that his inquiries into Iran's weapons program had reached a “;dead end.”;

The document describes a plan for measuring the output of a device called a neutron initiator, which has no use other than triggering a nuclear explosion. Intelligence agencies are treating it as if the very paper it was written on was itself radioactive.

Once burned when it accepted evidence about Iraq's search for uranium that turned out to be a forgery, the CIA has not declared whether it believes the document is real, according to intelligence officials from several countries. European spy agencies are similarly cautious.

“;Some people think this is the smoking gun,”; one senior European official said Tuesday, “;and others say it will be very hard to prove if it's authentic.”;

Inside intelligence agencies, the document has attracted much attention because its subject matter is familiar to anyone who has delved into Iran's atomic experiments: It describes a testing regime that would help Iran master the science of the initiator, a device to generate bursts of subatomic particles known as neutrons, which initiate and speed the chain reactions that lead to the detonation of a warhead.

When the document appeared in a public report on Sunday, it forced U.S. officials to begin to talk about it. But they insisted that even if it turns out to be genuine, it would only reinforce their strong belief that Iran had worked on a weapon.

“;This information's been sloshing around for well over a year,”; said one U.S. official, who insisted on anonymity because he was discussing sensitive intelligence information. “;It's not new to the intelligence people. They've taken account of it. If, in fact, the document's on the level, it shows the Iranians at some point were interested in testing an initiator. That's not a warhead or the core of a bomb. It's another reminder - as if one were needed - that the Iranians have a lot of explaining to do when it comes to things nuclear.”;

Concern that Iran could be working on neutron initiators goes back at least six years. As early as 2003, the inspection agency, the International Atomic Energy Agency, found evidence in Iran that raised suspicions.

In the current case, the most sensational claim is that the undated document was drafted in 2007. Because U.S. intelligence agencies have judged that Iran suspended its effort to build a nuclear warhead in 2003 - a conclusion that neither the Europeans nor the Israelis agree with - the 2007 date, if true, would mean that the U.S. assessment is wrong. And since the document describes a four-year research plan, the arms work, at least in theory, could be hitting its stride right now.

Not only intelligence agencies but also private nuclear experts see high risks in ringing alarm bells just yet.

The Institute for Science and International Security, a group in Washington that tracks nuclear proliferation, said in a report Monday that it “;urges caution and further assessment”; of the document, in particular to confirm its date. “;The document does not mention nuclear weapons,”; the report noted, “;and we have seen no evidence of aan Iranian decision to build them.”;

The Times of London claimed that the document showed that Iran “;is working on testing a key final component of a nuclear bomb.”; It subsequently made public the document in its original Persian as well as an English translation, starting a groundswell of global news coverage and expert reaction.

“;It's very troubling - if real,”; said Thomas B. Cochran, a senior scientist in the nuclear program of the Natural Resources Defense Council, a private group in Washington that tracks atomic arsenals.

Richard M. Barlow, an expert on nuclear proliferation and a former CIA analyst, said he found the document seemingly genuine. “;If it's a forgery,”; he said, “;it's very good.”;

Claims and evidence of Iranian interest in neutron initiators go back two decades, to the earliest days of Iran's suspected work on nuclear arms. In Vienna, international inspectors have filed many reports about how Iran began experiments in the late 1980s on generating neutrons with polonium-210 - a form of the metallic element that is highly radioactive.

The Iranians did the polonium experiments on the Tehran Research Reactor, the device at the center of the current political standoff over whether Iran will export most of its enriched uranium in exchange for fresh reactor fuel. The reactor can produce medical isotopes. Over the years, Iran has been less forthcoming about its potential military uses.

In multiple reports, beginning in 2004, the inspection agency warned that Iran's polonium research on the Tehran reactor had potential relevance for making “;a neutron initiator in some designs of nuclear weapons.”;

So too, in February 2005, an Iranian opposition group known as the National Council of Resistance of Iran said it had obtained evidence that Iran's polonium research was getting close to the point of producing a device that could “;trigger a chain reaction for a nuclear bomb.”;

This week, nuclear experts said the research outlined in the newly disclosed document implied that Iranian work on nuclear initiators might have advanced past the polonium model.