Socks fell to their lowest level in 10 weeks on Tuesday as talk of a second government stimulus plan heightened fears that the economy is not yet on the path to recovery and that the corporate earnings season starting this week will be weak.

A member of the Obama administration's economic advisory panel said the United States should plan to possibly provide a second round of stimulus funds to prop up the economy. The comments come as investors question earlier optimism for a quick recovery, which had driven stocks as much as 40 percent higher since early March.

It's clear that over the last three plus weeks that investors are becoming concerned that the recovery in the economy will not come as soon as expected and will not be as strong as expected, said Hugh Johnson, chief investment officer of Johnson Illington Advisors in Albany, New York.

When there's talk about another stimulus plan that adds fuel to that fire, it intensifies the concerns about the timing and strength of the recovery.

Cyclical stocks in the materials, energy, and industrial sectors, which had ridden a recent upswing in raw material prices on recovery hopes, led the market down as commodity prices eased. Copper, a barometer of global economic strength, fell nearly 2 percent.

Caterpillar Inc ,a maker of heavy machinery for construction and mining companies, shed 4.5 percent to $30.29.

The Dow Jones industrial average <.DJI> dropped 161.27 points, or 1.94 percent, to 8,163.60. The Standard & Poor's 500 Index <.SPX> fell 17.69 points, or 1.97 percent, to 881.03. The Nasdaq Composite Index <.IXIC> lost 41.23 points, or 2.31 percent, to 1,746.17.

The S&P 500 closed at its lowest level since May 1 while the Dow industrials closed at their lowest level since April 28.

An initial snapshot of the second-quarter performance of natural resource companies will come on Wednesday when Alcoa Inc kicks off quarterly earnings season. The aluminum producer, a Dow component, is expected to post a third consecutive quarterly loss.

S&P 500 corporate earnings are expected by analysts to have declined about 36 percent from a year ago, according to data compiled by Thomson Reuters. That would be roughly the same as the decline seen in the first quarter.

Doubts about the strength of an economic recovery and subsequent demand for oil have sent crude prices tumbling in the last week. New York crude fell 1.8 percent on Tuesday and is down about 14 percent from the intraday peak hit on June 30. Its slide has pressured energy stocks.

Oil services company Schlumberger Ltd fell 4.4 percent to $49.20 while blue chip Exxon Mobil Corp lost 2.3 percent to $66.56. The S&P energy sector <.GSPE> index lost 2.5 percent.

Non-cyclical areas of the market, which have been stronger in recent weeks as investors sought out companies better positioned to weather a weak economy, initially withstood the sell-off on Tuesday. But by the end of the day even the defensive sectors fell victim to selling.

Health care, a classic defensive sector, traded in positive territory for most of the day but by the close the S&P healthcare index <.GSPA> fell 0.3 percent -- still outperforming the wider market.

Drug maker Pfizer Inc

, one of the few Dow stocks to finish in positive territory, edged up 0.1 percent to $14.59.

A rally in the broad S&P 500 index that had boosted it about 40 percent from 12-year lows hit in early March has wilted in the last month as investors sought stronger evidence that economic conditions were improving.

Trading was below average on the New York Stock Exchange, with about 1.11 billion shares changing hands, under last year's estimated daily average of 1.49 billion, while on Nasdaq, about 2.04 billion shares traded, below last year's daily average of 2.28 billion.

Declining stocks outnumbered advancing ones on the NYSE by 4 to 1 while decliners beat advancers on the Nasdaq by about 10 to 3.

(Editing by Leslie Adler)