Renewed questions about corporate impropriety, this time involving Citigroup and AOL Time Warner, pressured stocks. So did news that two brokerages cut revenue estimates for several semiconductor companies.

But the market was mostly feeling the brunt of profit-taking, analysts said.

The Dow closed down 180.68, or 2 percent, at 8,872.96, according to preliminary calculations. The drop erased a two-day gain of 181 points that pushed the index to 9,053.64 yesterday, the first time it closed above 9,000 since July 9. The broader market was also lower. The Nasdaq composite index fell 42.36, or 3 percent, to 1,380.59. The Standard & Poor's 500 index slipped 21.84, or 2.3 percent, to 940.86.

Analysts said investors have been more optimistic after three straight weeks of gains among the Dow, Nasdaq and S&P, which hasn't happened since the three-week period ending Nov. 23.

Such a feat is impressive, analysts say, particularly since August typically underperforms other months and has lacked significant good news to trigger a rally.

The Dow has risen 10.6 percent since July 19, the last time it had a losing week. The Nasdaq composite has gained 10.6 percent and the S&P 500 index advanced 8.9 percent since Aug. 2, when they last posted weekly losses.

Still, analysts say the markets remain vulnerable to bursts of profit-taking until investors have more concrete evidence that an economic turnaround is under way. Questions also linger about corporate corruption, they said.

Such questions weighed on several companies today, including Citigroup, which fell $1.18 to $34, on a report in The Wall Street Journal that the New York attorney general's office was widening its probe into research practices at Salomon Smith Barney by examining how Citigroup won a lucrative financing deal from AT&T.

AOL Time Warner slipped $1.31 to $12.76, on reports that the largest portion of $49 million in questionable ad revenue being investigated by the Securities and Exchange Commission involved dealings with now-bankrupt WorldCom.