After a decade of calamitous western wars in the wider Middle East, the signs are becoming ever more ominous that we're heading for another. And, hard as it is to credit, the same discredited arguments used to justify the disasters of Iraq and Afghanistan – from weapons of mass destruction to sponsorship of terrorism and fundamentalist fanatics – are now being used to make the case for an attack on Iran.

War talk about Iran and its nuclear programme has been going on for so long it might be tempting to dismiss it as bluster. The mixed messages about Iran coming from the US and Israeli governments in recent weeks have become increasingly contradictory and bewildering. Maybe it's all a game of bluff and psychological warfare. Perhaps Iran's offer of new talks or this week's atomic energy inspectors' visit might lead to a breakthrough.

But the mood music has become more menacing. US defence secretary Leon Panetta has let it be known there is a "strong likelihood" Israel will attack Iran between April and June, even as Barack Obama says no Israeli decision has yet been taken. US officials told the Guardian last week they believed the administration would be left with "no alternative" but to attack Iran or watch Israel do so later this year.

Meanwhile, a US-Israeli stealth war is already raging on the ground, including covert assassinations of scientists, cyber warfare and attacks on military and missile installations. And Britain and France have successfully dragooned the EU into ramping up sanctions on Iran's economic life-blood of oil exports as a buildup of western military forces continues in the Gulf.

Any of this could easily be regarded as an act of war against Iran – and Iranian retaliation used as the pretext for a more direct military assault, as the risk of escalation grows. But instead of challenging what is a profoundly dangerous path to full-scale regional conflict – with or without western intervention in Iran's ally, Syria – the bulk of the western media and political class is busy softening up the public to accept another war as the unfortunate consequence of Iranian intransigence.

When it was reported that British officials expected the Cameron government to take part in a US attack on Iran, it passed with barely a murmur. In a parliamentary debate on Monday, only six votes were mustered to press for the threat of attack on Iran to be withdrawn. The Times claimed yesterday it to be "beyond doubt" that Iran "is trying to develop a nuclear weapon", even though neither the US nor the IAEA has managed to prove any such thing.

And even when US and British leaders have called for Israeli restraint, as William Hague and US joint chiefs of staff chairman Martin Dempsey have done in recent days, the issue is only one of timing. Military force would, they say, be "premature" and unwise "at this point".

If an attack is launched by Israel or the US, it would not just be an act of criminal aggression, but of wanton destructive stupidity. As Michael Clarke, director of the British defence establishment's Royal United Services Institute, points out, such an attack would be entirely illegal: "There is no basis in international law for preventative, rather than pre-emptive, war."

It would also be guaranteed to trigger a regional conflagration with uncontrollable global consequences. Iran could be expected to retaliate against Israel, the US and its allies, both directly and indirectly, and block the fifth of international oil supplies shipped through the Strait of Hormuz. The trail of death, destruction and economic havoc would be awesome.

But while in the case of Iraq an attack was launched over weapons of mass destruction that didn't in fact exist, the US isn't even claiming that Iran is attempting to build a bomb. "Are they trying to develop a nuclear weapon? No," Panetta said bluntly last month. Israeli intelligence is said to be of the same view. Unlike Israel itself, which has had nuclear weapons for decades, it believes the Iranian leadership has taken no decision to go nuclear.

The issue, instead, is whether Iran – which has always insisted it doesn't want nuclear weapons – might develop the capability to build them. So Iran – surrounded by US bases and occupation troops, nuclear-armed states from Israel to Pakistan and Gulf autocracies begging the Americans to "cut off the head of the snake" – is threatened with a military onslaught because of a future potential the aggressor states have long ago turned into reality.

Such a capability wouldn't be the "existential threat" Israeli politicians have claimed. It might, of course, blunt Israel's strategic edge. Or as Matthew Kroenig, the US defence secretary's special adviser until last summer, spelled it out recently, a nuclear Iran "would immediately limit US freedom of action in the Middle East". Which gets to the heart of the matter: freedom of action in the Middle East is the prerogative of the US and its allies, not independent Middle Eastern states.

But if the western powers and Israel are really concerned about the threat of a nuclear arms race in the region, they could throw their weight behind negotiations to acheive a nuclear-free Middle East – which most Israelis favour.

What is clear, as both US and Israeli officials acknowledge, is that neither sanctions nor war are likely to divert Iran from its nuclear programme. Military attack can set it back – along with the prospects for progressive change in Iran – but would offer the strongest incentive possible for Iranian leaders to take the decision they haven't yet done and develop nuclear weapons.

Obama has every interest in heading off an Israeli attack on Iran that would draw in the US, until at least until after the presidential election. But as the sabre-rattling, crippling sanctions and covert attacks increase, so do the risks of stumbling into an accidental war. A military confrontation in the Strait of Hormuz in the next two or three months is now "quite likely", Clarke believes: "western policy towards Iran is a slow-motion road accident".

There is another factor driving towards war. The more they talk up the supposed threat from Iran's nuclear programme and the military option, the more US and Israeli leaders risk undermining their own credibility if they end up doing nothing. A potentially catastrophic attack isn't inevitable, but it's becoming perilously more likely all the time.

Twitter: @SeumasMilne