New York ? News of a government investigation at Johnson & Johnson gave Wall Street another reason for a selloff Friday, and the Dow Jones industrials fell as much as 308 points well below their post-terrorist attack low.

The losses were compounded by selling due to a reconfiguration of the Standard & Poor’s 500 index, as well as the expiration of some index and stock options.

By midafternoon, the Dow had regained some ground and was down 265.83, or 3.2 percent, at 8,143.66. That was 92.15 points below its Sept. 21 finish of 8,235.81.

Broader stock indicators, which have been trading below their Sept. 21 lows for a while, also retreated. The Nasdaq composite index fell 26.63, or 2.0 percent, to 1,330.32, and the S&P was off 22.48, or 2.6 percent, at 859.08.

The S&P, which closed below 900 Thursday for the first time in nearly five years, will replace all foreign stocks with domestic ones as of the end of the session. As a result, funds that track the index have to adjust their portfolios to match.

“It’s very volatile out there,” said Robert Harrington, head of listed block trading at UBS Warburg. “The news out there isn’t so good, and the options expiration and S&P changes are putting pressure on the market.”

The losses put the three indexes on track for their ninth lower close in 10 sessions and ninth straight losing week and reflected trends that have dogged stocks for two months now. Investors, fed up with accounting scandals and concerned that business isn’t recovering strongly or quickly enough, have been unloading shares for fear stock prices will fall further.

Johnson & Johnson dropped $6.48 to $43.25 after The New York Times reported that the FDA and the Justice Department investigating a company factory that makes an anemia drug linked to illnesses in Europe and Canada. The company told the newspaper that it was aware of a government investigation, but did not know its precise nature.

A new slew of earnings reports also captured investors’ attention.

Merck rose 29 cents to $42.29 after reporting second-quarter results in line with expectations despite a 4 percent drop in profits.

In the tech sector, Microsoft fell $1.15 to $49.96 after beating analysts’ expectations but reducing its forecast for later this year.

Sun Microsystems fell $1.64 to $4.16, a new 52-week low, after reporting results in line with expectations, but indicating its current quarter’s results are being affected by difficult business conditions.

Financial stocks also pulled back. American Express dropped $1.73 to $31.80.

Friday’s pullback wasn’t surprising, given the market’s recent habit of selling off on any even remotely negative news. Stocks have fallen sharply in recent sessions as investors avoid the markets for fear their investments will lose more value.

The intensity of the selling has also increased because of computer trading programs that kick in when stock prices reach certain levels and sell or buy hundreds of thousands of shares at a time.

Declining issues led advancers 3 to 1 on the New York Stock Exchange. Volume came to nearly 1.30 billion shares, compared with 1.08 billion shares at the same point Thursday.

The Russell 2000 index fell 6.64 to 390.07.

Overseas, Japan’s Nikkei stock average slid 2.8 percent. In Europe, Germany’s DAX index fell 4.6 percent, Britain’s FTSE 100 slipped 4.6 percent, and France’s CAC-40 lost 5.4 percent.