"The plan we are executing is aggressive. It is the right plan. It will take time to have its full impact. It is flexible enough to adapt as the situation changes. And it is big enough to work," Bush said.

He also noted that the Federal Reserve has injected hundreds of billions into the system and with other central banks has made interest-rate cuts that should help thaw frozen credit markets and enable loans to flow again.

Government insurance on bank and credit union deposit accounts has been raised to $250,000 and the Treasury is offering insurance for the first time for money-market funds, he added.

"The federal government has a comprehensive strategy and the tools necessary to address the challenges in our economy," Bush said.

While he sought to reassure Americans that the government is doing all it can, Bush also acknowledged mounting worry among people about their retirement and investment accounts.

Bush said his administration had launched initiatives that "have helped more than 2 million Americans stay in their homes."

He also noted "rigorous enforcement" steps taken by the Securities and Exchange Commission to make sure that some investors don't "take advantage of the crisis to illegally manipulate the stock market."

Stock market volatility continued, with the Dow Jones industrials falling nearly 700 points soon after trading began, regaining all of that deficit to show an advance and then turning lower again.

"Over the past few days," Bush said, "we have witnessed a startling drop in the stock market, much of it driven by uncertainty and fear. This has been a deeply unsettling period for the American people."