Worries about the corporate sector sent stocks on Wall Street lower again on Wednesday, with the Dow Jones industrials dropping more than 400 points before recovering slightly. Improvements in the credit markets — including the third straight day of declines in bank borrowing rates — did little to placate stock investors who are eying the corporate consequences of an economy that many economists believe is already in a recession. Earnings reports have been weak this week, and many companies have warned about lower sales and a bleak outlook for the remainder of the year. The problems have appeared in a range of industries. The aviation giant Boeing saw profits fall 38 percent last quarter. Merck, the pharmaceutical company, posted a 28 percent drop in net income and will cut jobs. The North Carolina-based bank Wachovia, which was recently acquired by Wells Fargo, suffered a $23.7 billion net loss. At noon, the broad Standard & Poor’s 500-stock index was down 3.2 percent. The Nasdaq composite index was off about 1.9 percent, despite gains in shares of Apple and Yahoo. The Dow, after falling more than 200 points on Tuesday, was off 284.59, at 8,749.07, with 29 of the 30 components of the index in retreat. Oil prices hit a low for the year, falling below $68 a barrel. The cost at which bank lends to one another, as measured by the key Libor rate, fell again for 3-month and overnight loans. The market jitters began earlier overseas. In late afternoon trading, the DJ Euro Stoxx 50 index, a barometer of euro zone blue chips, was down 5.4 percent, while the FTSE 100 index in London lost 4.5 percent. The CAC-40 in Paris was off 5.1 percent and the DAX in Frankfurt slipped 4.5 percent. In Tokyo, the benchmark Nikkei 225 stock average plunged 6.8 percent after three days of gains as the yen surged. NEC Electronics plummeted about 20 percent. The electronics company shocked investors by slashing its annual operating profit forecast by 90 percent to 1 billion yen, or $10 million, citing weak demand. In Sydney, the S&P/ASX 200 closed 3.4 percent lower. The Hang Seng index in Hong Kong closed more than 5 percent lower, as Citic Pacific fell 24 percent. The company this week predicted a trading loss of up to $2 billion caused by what it said were unauthorized bets on foreign exchange markets. “The main story is that deleveraging among financial institutions is continuing,” Derek Halpenny, senior currency economist at Bank of Tokyo-Mitsubishi UFJ in London, said. “Banks worried about funding are selling assets to reduce their balance sheets.” The wave of coordinated global bailouts has helped banks’ capital ratios, he noted, but there is a painful readjustment under way that will require some time to work through. The dollar soared against European currencies. The euro fell to $1.2858, its lowest since November 2006, from $1.3063 late Tuesday in New York. The dollar rose to 1.1665 Swiss francs from 1.1512 francs. Expectations that European central bankers will cut interest rates to stimulate growth has reduced the incentive for investors to buy short-term assets based in those currencies. In Britain, the pound fell to $1.6260 from $1.6707, after the Bank of England governor, Mervyn King, warned that the British currency could come under pressure, and acknowledged that the country had entered what could be a painful recession. “Taken together, the combination of a squeeze on real take-home pay and a decline in the availability of credit poses the risk of a sharp and prolonged slowdown in domestic demand,” Mr. King said Tuesday in Leeds, England. But the yen trumped all other currencies. The dollar fell to 99.27 yen from 100.13, while the euro fell to 127.69 from 131.58. Mr. Halpenny said the yen was benefiting from its position as a safe-haven currency, supported by the fact that Japan is running a large current-account surplus. United States crude oil futures for December delivery fell $3.22, or 4.5 percent, to $68.96 a barrel.