All these companies’ mushrooming needs reflect just how hard it is to stanch the flow of losses as the economy deteriorates. Even though the government’s finances are being stretched — and still more aid might be needed in the future — it is being forced to fill the growing holes in the finances of these companies out of fear that the demise of an important company could set off a chain reaction.

The deepening global downturn is dragging down all kinds of businesses, and, with no bottom to the recession in sight, investors sent the the Dow industrials down 250.89 points, or 3.7 percent, to 7,114.78, a 3.7 percent drop for the day and a loss of about 50 percent from their peak in the fall of 2007. Asian markets followed suit on Tuesday by flirting with the lows they hit last October, with stocks in Hong Kong dropping more than 3 percent, and Japan's Nikkei 225 index dropping more than 2 percent before rebounding slightly.

In an unexpectedly assertive joint statement after two weeks of bank stock declines, the Treasury Department, the Federal Reserve and federal bank regulatory agencies announced that the government might demand a direct ownership stake in major banks that do not have enough capital to weather a deeper downturn. The government will begin conducting a test of the banks’ financial health this week.

Administration officials emphasized that nationalizing any of the major banks was their least favorite solution to the banking crisis, but they acknowledged that some banks might be both too big to fail and too fragile to endure another round of shocks without substantial help.

Banks that fail the test will have to raise additional capital. If they are unable to raise capital in the private market, they would have to take money from the government in exchange for preferred stock that would be convertible into common shares, thus giving the government a bigger stake.