Markets awaiting more stimulus for the US economy will likely be disappointed Friday when Federal Reserve Chairman Ben Bernanke delivers a key annual speech, analysts said.

With economic data still mixed and the Fed policy board divided over the need for action, the chief US central banker is expected to keep his options open, despite clamor for a new "QE3" injection of money to help boost growth.

In the past two years Bernanke has used the annual central banking conference at Jackson Hole, Wyoming to telegraph the Fed's direction.

In 2010 he signaled the coming of the $600 billion QE2 quantitative easing program, which gave a strong boost to markets, though its effect petered out after a year.

Last year he suggested a slighter effort was forthcoming, while making a strong call for the government to take action to boost growth and not depend on the Fed.

This year markets should expect less, even if economic growth remains tepid, analysts say.

Bernanke opens the Jackson Hole conference, attended by central bankers from around the world, at 1400 GMT Friday, after weeks of speculation over what he will say.

"We expect it will be anti-climactic," said Jim O'Sullivan of High Frequency Economics.

"We expect Mr. Bernanke will sound dovish," showing disappointment in the pace of growth and warning about potential pitfalls.

"However, he is unlikely to send a definitive signal on what measures, if any, are likely," O'Sullivan said.

Bernanke and the Federal Open Market Committee, the central bank's policy board, are clearly concerned about the slow pace of economic expansion and job creation, and the vulnerability of the country to external shocks.

Minutes from the FOMC's July 31-August 1 meeting showed them leaning more toward a new stimulus than had been expected.

Bernanke himself seemed to confirm that drift when he told a member of Congress last week in a letter that "there is scope for further action by the Federal Reserve to ease financial conditions and strengthen the recovery."

But, he cautioned, the FOMC will act on economic and market data and will only "provide additional accommodation as needed" to help the economy.

The data since the last FOMC meeting has been unclear.

Data on the housing market has shown significant improvement; on jobs it is flat; industrial production seems to have declined slightly; and consumer spending is a little stronger, but with weak signs.

Meanwhile, the sharp slowdown in China and Europe's move back toward recession have meant that neither can be expected to spend on goods from reinvigorated US industries.

On Wednesday the Fed's Beige Book assessment of current regional economic conditions, a key input for the next FOMC meeting on September 12-13, said growth remained weak.

Analysts disagreed, however, on whether the cryptic language -- "economic activity continued to expand gradually in July and early August across most regions and sectors" -- meant the Fed saw things getting better or worse.

The direction of the lean is key.

The minutes of the previous FOMC meeting suggested that there was an increase in the number of the group's 12 voting members in favor of more "monetary accommodation", meaning sending signals or taking action that would help push down long-term interest rates.

But the minutes only said that "many members" were of that mind, leaving analysts trying to understand if that meant most members or not.

James Bullard, one of the more conservative FOMC members, admitted last week that, generally, "things haven't been where we would like them to be."

But at the same time, he said that the views in the last meeting were outdated "because we have some data since then that has been a bit stronger."

Joseph LaVorgna of Deutsche Bank said that suggests the Fed will remain in a holding pattern as it looks for more data signals.

"While we think the chairman may take this opportunity to elaborate on remaining policy options for policymakers, we do not believe he will pre-commit to action at the September 12-13 FOMC meeting," he said.