Washington  - Amidst growing resistance in Congress to a proposed urgent, mammoth bailout plan for Wall Street, US President George W Bush was to speak later Wednesday on the economy, the White House said.

The speech at 9 pm (0100 GMT Thursday) comes after repeated calls from Congress and the public for a more complete explanation of why the White House is so anxious to push through an emergency 700- billion-dollar plan by week's end.

"There are a lot of people out there who still don't understand why it is necessary to do anything," said Representative Mel Watt of North Carolina at a House financial services committee hearing.

He said it was time for the administration to be "honest" with the public.

The rescue plan equals about one-quarter of the 2.9 trillion- dollar budget for 2008. The administration hopes to pass the plan ahead of a congressional recess set to begin Friday ahead of November 4 elections.

On Monday, Bush warned that "failure to act would have broad consequences far beyond Wall Street." Last week, he said that credit availability for everything from houses and cars to student loans could dry up, bringing to a complete halt the borrowing on which much of the US economy is based.

"These are risks that America cannot afford to take," Bush said last week.

Treasury Secretary Henry Paulson and Federal Reserve chief Ben Bernanke have met stiff resistance and criticism this week as they laid out details of the bailout plan to Congress.

They submitted a barebones three-page outline of the programme late last week, although it had been under development for at least three months, according to the White House.

The plan calls for the US government to buy up toxic mortgage debts and related unregulated securities in order to free up the flow of credit, which the White House says is even affecting the ability of some employers to meet payroll.

Earlier Wednesday, Bernanke warned Congress that the stability of the US financial system faced "grave threats" and painted a gloomy picture for future growth, saying "greater-than-normal uncertainty" surrounded any forecast of the pace of activity.

"The downside risks to the outlook ... remain a significant concern," Bernanke told the Joint Economic Committee of the US Congress.

"If financial conditions fail to improve for a protracted period, the implications for the broader economy could be quite adverse," he said. "I urge the Congress to act quickly to address the grave threats to financial stability that we currently face."

Bernanke projected continuing high inflation, a weakening labour market and decelerated economic activity. Since November 2007, the country has lost 770,000 jobs and boosted unemployment to 6.1 per cent.

The plan would be the largest government intervention in capital markets since the Great Depression of the 1930s, and has provoked public anger that tax dollars would be used to clean up years of unregulated Wall Street greed.

Senate banking committee chairman Chris Dodd, a member of the majority Democratic Party, Tuesday questioned the wisdom of throwing 700 billion dollars into the market without any quid pro quo from the firms.

"After reading this proposal, I can only conclude that it is not just our economy that is at risk, but our Constitution as well," said Dodd, calling the crisis "an extraordinary and perilous moment in our nation's history."

Senator Richard Shelby, the senior Republican on the panel and an outspoken critic of his own president's proposal, vowed he would not "sign off on something of this magnitude" until he knew that alternatives had been exhausted.

"The Treasury's plan ... is aimed at rescuing the same financial institutions that created this crisis with the sloppy underwriting and reckless disregard for the risk they were creating, taking or passing on to others," Shelby said Tuesday. (dpa)