The Bank of Canada has cut a key short-term interest rate about as low as it can go in what is becoming a frantic effort to spark recovery from a recession it admits it has misjudged.

The central bank did what virtually every private sector economist advised it to do Tuesday morning, slashing the trend-setting overnight rate to 0.5 per cent into uncharted territory.

But bank governor Mark Carney, who was criticized for being overly rosy in his January economic outlook, now says that even at such unheard-of lows, the stimulus provided by traditional monetary policy is likely not enough.

And he said the bank now sees recovery coming later than it had projected, possibly in early 2010.

‘‘Given the low level of the target for the overnight rate, the bank is refining the approach it would take to provide additional monetary stimulus, if required, through credit and quantitative easing,’’ Carney wrote in a statement.

The central banker does not give examples of specific measures, but BMO deputy chief economist Doug Porter said the bank is considering a process whereby it injects money into the system buy buying up assets such as government bonds, asset-backed commercial paper and even government bonds directly.

‘‘Simply put, the bank is preparing to pull out all the stops to support the economy,’’ he said.

Canada’s major banks appeared ready to play ball with Carney: shortly after the announcement, Royal Bank (TSX:RY), Bank of Montreal (TSX:BMO), TD Bank (TSX:TD) and CIBC (TSX:CM) announced that they would cut their prime rates in step with the central bank.

The reference to non-traditional monetary measures confirms that Carney knows he has exhausted interest rate cuts as a means of stimulating the economy out of a deepening and increasingly stubborn recession.

Darcy Briggs of Bissell Investment Management in Calgary said the bank could trim rates to 0.25 per cent — as the U.S. Federal Reserve has done — but ‘‘practically, what would that do?’’

As former Liberal cabinet minister and economist Doug Peters wrote last week: ‘‘Interest rates that count, such as interbank lending rates, mortgage lending rates, bank commercial lending rates, are all unusually high, especially considering that inflation is also very close to zero.’’

The other surprise was that Carney appeared to back off his relatively rosy forecast for the Canadian economy, which envisioned growth returning in the third quarter of this year and rebounding to 3.8 per cent next year.

‘‘The outlook for the global economy has continued to deteriorate since the bank’s January... update, with weaker-than-expected activity in major economies,’’ Carney said Tuesday.

‘‘National accounts data for the fourth quarter of 2008 and other indicators of aggregate demand point to a sharper decline in Canadian economic activity and a larger output gap through the first half of 2009 than projected in January.’’

Carney said potential delays in stabilizing the global financial system, along with low consumer confidence and larger hit on household wealth, ‘‘could mean that the output gap will not begin to close until early 2010.’’

Tuesday’s statement does not officially alter the forecast, but strongly implies that both this year’s 1.2 per cent contraction will be worse and that the recession may last until next year.

Most economic indicators have come in far weaker since January’s much-criticized bank outlook, including Monday’s report that the Canadian economy has shrunk by 3.4 per cent in the last quarter of 2008, far worse than the bank’s negative 2.3 per cent projections.

As well, Canada lost 129,000 jobs in January, a massive amount, which Carney did not know when he made his forecast.

But possibly the most critical factor is that the global economy, especially among industrialized nations, appears to be in free-fall.

The fourth quarter saw GDP fall by 6.2 per cent in the United States, six per cent in the United Kingdom, 5.7 per cent in the Eurozone, 10.3 per cent in Mexico and a massive 12.7 per cent in Japan.

And far from stabilizing, the U.S. financial system is lurching from crisis to crisis. On Monday, the U.S. government said it was adding another $30 billion to the bail-out package for the giant insurance company American International Group Inc. after it reported a staggering US$61.7-billion in quarterly losses.

‘‘Stabilization of the global financial system remains a precondition for the global and Canadian economic recoveries,’’ Carney noted in his statement.

Carney also forecast that inflation will likely be lower than expected this year.