If there is a silver lining to the Treasury market’s gyrations, it is that the United States can borrow money more cheaply from investors, whether they be the governments of China or Japan, or big fund managers. That could help Washington finance various programs intended to revive the ailing economy.

Borrowing by the Treasury has already ballooned since Congress approved the $700 billion financial rescue plan, and policy makers expect the federal budget deficit to swell further next year as the Big Three automakers and other industries look for support.

“That sucking sound is all the world’s capital going into the U.S. Treasury market,” Mr. Yardeni said, “which means the Treasury and the Fed can tap into that liquidity pool to finance TARP and offer mortgages at 4.5 percent.”

While that may offset some of the expense of the bailouts, economists say the fact that the United States must borrow so much to prop up large parts of the economy is a big cause for concern.

There are several explanations for the flight to safety in the bond market. The world of short-term money market funds, for instance, is still reeling from troubles at the Reserve Primary Fund, a money market fund frozen in September after it lost money on investments in Lehman Brothers. Since then, individual and large investors have put more than $200 billion into money funds that only invest in safe Treasury bills, according to iMoneyNet, a financial data publisher. At the same time, investors have withdrawn nearly $400 billion from prime funds.

That has forced portfolio managers to buy Treasury bills, driving down yields. “That group of investors has to invest in something,” said Max Bublitz, chief strategist at SCM Advisors. “They don’t have the luxury of saying, ‘I will stick it in the mattress.’ ”

Yields for longer term Treasury securities have also slumped, with the 10-year now yielding 2.64 percent, down from 2.7 percent Monday and 3.75 percent a month earlier. That decline appears to reflect several other forces. Many investors are seeking safety because they believe that the economy is in its worst recession since the Depression. Rather than inflation, which was a worry for some a few months ago, many are now worried about deflation, or falling prices.