That, of course, is not quite the view taken in Washington, where the Secretary of State, Warren Christopher, claims Iran is "a major threat to United States' interests and international security" and where President Bill Clinton was apparently so worried that he turned up in Moscow with a bunch of classified documents "proving" Iran's determination get its hands on the bomb.
''Mr Clinton brought some papers to Mr Yeltsin in Moscow which he considered good proof of Iran's nuclear intentions," Mr Tretyakov says. "But that was not the first time the Americans have brought papers like these to us. I was involved in the last investigation of this kind - when we were planning to sign a framework nuclear agreement with Iran. We investigated all this very carefully - many organisations participated in this."
And was the KGB among these organisations, I asked. More laughter. "We found nothing! And, believe me, Iran's military capability is of no less concern to Russia than it is to the United States - because we are much closer to Iran than America. I don't know what Mr Clinton brought to Moscow in the latest documents - but we are very careful."
The embassy stands in a compound originally staked out when a Tsarist soldier gambled with a Qajar prince and won the territory by betting with his last possession, his military sword. In one of its rooms Stalin, Roosevelt and Churchill argued over the time and location of the second front against Nazi Germany.
''I'll be crystal clear in my answers to you,'' Mr Tretyakov said, chain- smoking, and sipping coffee and cola. ''The history of Russian-Iranian nuclear co-operation goes back to August 1992, when the framework agreement between Russia and Iran in the peaceful uses of nuclear energy was originally signed.
"Several rounds of talks were held here in Tehran between our own minister of atomic energy, Vladimir Mikhaelov, and Reza Amrollahi, the director of the Iranian Atomic Energy Organisation. The result of these talks was a contract signed last January for the completion of an old project started by the Germans before the 1979 revolution, the nuclear power station at Bushehr.''
The embassy's first secretary was at Mr Tretyakov's side, reminding his ambassador of dates and names. "We agreed to fulfil our obligations on the Bushehr nuclear plant. And when we decided to do this, we kept in mind two major points. Firstly, that Iran was and is a signatory to the Non-Proliferation Treaty; secondly, Iran has a treaty with the Atomic Energy Agency regarding guarantees.
"Many times, experts of the agency visited the Islamic Republic of Iran and were given all possible opportunities by the Iranian authorities to observe any kind of objects which might be of concern to them. But they found nothing that could prove Iran had military aspirations in the nuclear field."
The Russians can provide a detailed analysis of Iran's economic progress - some might call it decline - since the revolution. In 1979, with a population of 76 million and an oil price of $30 a barrel - with oil output of 4 million barrels a day, two thirds of it for export - Iran had no foreign debts and possessed pounds 23bn in gold and foreign reserve assets.
Today, with oil at $14 or $15 a barrel, it has an output of 3.2 million barrels a day, exports of between 2.2 and 2.3 barrels and a potential foreign debt of $46bn (pounds 29bn), all contracted since 1989. The Russian view - not expressed by the ambassador - is that the price of the Islamic revolution was to set back Iran's technological progress around 40 years.
Nor does Mr Tretyakov have time for the US argument that Iran's nuclear ambitions are channelled through a military structure that runs parallel to, but separate from, Mr Amrollahi's own atomic organisation, a weapons procurement office run by Iran's Defence Ministry Organisation.
''We are convinced that Iran has no ambitions in the nuclear field. You know, when someone wants to develop a nuclear bomb, they must have the political will and the technological base. The Iranians don't have such aspirations - but even if they had, I think it would take them 50 years.''
According to Mr Tretyakov, around 150 Russian technicians are now at the Bushehr nuclear plant, badly damaged by Iraqi fighter-bombers in the 1980-88 war. "Our technicians are checking the condition of the concrete, the steel structures and looking at the equipment delivered by the Germans that was lying in the open air for 15 years.
"Our contract will be implemented at the end of this year because, by this time, preliminary negotiations will be complete. Iranian payments will be in tranches. The whole work will take approximately four years - no credits, nothing. This is a cash deal, US dollars, not Iranian riyals."
There was another smile here, a gesture to the inflationary riyal and President Ali Akbar Hashemi Rafsanjani's current efforts to peg Iran's currency at 3,000 to the dollar. ''Iran has economic problems resolving her debts.'' he said. ''It managed to reschedule its debt with Germany, Japan and a majority of Western countries. But we can't do things the same way because we don't have export insurance cover. We are trying to solve this problem. Iran's current debt to Russia stands at more than $450m, which to some extent restrict our economic co-operation. Bushehr is different. The Iranians know the cash deal quite well - no money, no deal."
A diplomat wants to show me the room in which the wartime summit was held, a bust of Lenin on one wall, ''restored exactly as it was when the Big Three met here'', its 100-year-old gold-framed mirrors - minus the Tsarist double-headed eagle - still hanging as they did when reflecting the leaders of the three superpowers 52 years ago.
Ayatollah Khomeini didn't like Stalin very much, condemning the "aristocratic ceremonies" at the 1943 conference and calling Stalin "the so-called bright face of the [Communist] party" who brought a cow to Tehran from Moscow to provide him with fresh milk.
Not surprisingly, the one thing taken down from the summit room for this year's VE anniversary was the plaster bust of Stalin himself. Like Iran's alleged nuclear ambitions - out of sight, out of mind.