An anxious world will on Tuesday get the first reliable reading of the US economy's pulse since the terrorist attacks of September 11.

The consumer confidence report, a monthly survey of 5,000 American households conducted by the Conference Board, the independent research group, is always scrutinised closely by economists.

Though it does not provide a perfect guide to the future path of consumption - the component of aggregate demand that accounts for two thirds of all economic activity - it does broadly track retail sales. Given the fact that it is published more or less concurrently, while retail sales figures are not published until the middle of the month after the month whose spending they measure, it is as close to being a real-time indicator of consumption as US statistics-watchers have.

The September report, published at 10am Eastern Time on Tuesday, will indicate just how severe the blow to confidence has been from the devastation in New York and Washington.

Before the attacks, there had been mixed signals about how consumers were responding to evidence of the economic slowdown already in place over the last year. Confidence dropped sharply last autumn and winter but by the spring there were signs that it might be starting to stabilise, at levels above those usually associated with a recession. The steep decline in year-on-year growth in retail sales also levelled off around the same time.

But from July, confidence drifted lower again. Some smaller surveys of consumer confidence indicated that in the first few days of September, before the attacks but after the disturbing news of a steep rise in unemployment, consumers had become much less optimistic about the economy.

The pattern of consumer confidence historically suggests this evanescent but critical element in the economic picture is driven by long-term fundamental variables, such as unemployment and income and wage growth, but is subject also to violent cross-currents from shocks - financial and political.

The index is broken into two components - consumers' assessment of present conditions and their expectations about future economic developments. The steep drop at the end of last year was driven largely by a decline in the expectations index while present conditions were thought to be deteriorating but not so rapidly.

The details of the report - with consumer responses on job prospects, their own financial circumstances and others - seemed to suggest this declining optimism was tracking the fallout in the stock market, especially the technology sector, and the explosive headlines it was producing last autumn and winter.

In July and August, however, while the expectations component of the index held up well, it was the present situation about which consumers expressed most concern - especially what they saw as increasingly difficult labour market conditions.

With employment conditions deteriorating still further - even before the September 11 attacks - the outlook for consumer confidence this autumn already seemed to be growing bleaker.

Curiously, however, smaller surveys taken since the attack have suggested confidence stayed resilient or even rebounded slightly after September 11. A Gallup poll conducted last week showed a sharp improvement in consumers' expectations.

But Tuesday's report - and subsequent confidence figures - will prove more reliable. These previous brief snapshots were taken after the attacks but before last week's stock market decline - the largest weekly drop since the great depression. It will be much harder for confidence to hold up in the face of such financial weakness.