* DuPont's earnings forecast, job cuts weigh on oil
* Brent tests support at 100-day moving average
* U.S. crude stocks likely rose last week - analyst poll
* Coming Up: EIA oil data 10:30 a.m. EDT Wednesday (Adds API data paragraphs 18-21)
By Robert Gibbons
NEW YORK, Oct 23 (Reuters) - Oil prices fell sharply on Tuesday as slowing global economic growth, Europe's continuing debt crisis and weak earnings forecasts from U.S. corporations pressured commodities and equities.
Brent fell for a sixth straight session and U.S. crude was down for a fourth consecutive day to settle at a three-month low.
Evidence of slowing economic growth and an improving crude oil supply picture continued to counter any potential lift from Middle East turmoil and Iran's dispute with Israel and the West over Tehran's nuclear program.
Chemical company DuPont lowered its earnings forecast, announced 1,500 job cuts and posted lower-than-expected profit, pressuring equities, oil and other commodities.
The Thomson Reuters-Jefferies CRB index, a gauge widely followed by commodity investors, fell 1.2 percent.
DuPont's gloomy outlook came a day after heavy machinery maker Caterpillar Inc warned that the U.S. economy was slowing faster than expected.
Rising Spanish borrowing costs and slumping business morale in France's manufacturing sector added to concerns about Europe's debt crisis and sputtering economic growth.
"The main bearish driver is the state of the economy," said Filip Petersson, an analyst at SEB in Stockholm. "And that's taken all markets down quite a bit."
TransCanada Corp's Monday restart of its Keystone pipeline carrying crude oil from Canada to the United States added pressure on oil futures.
Brent December crude fell $1.19 to settle at $108.25 a barrel, its lowest settlement since Oct. 3. It slumped to $107.31, its lowest level since Sept. 20 and below the 100-day moving average of $107.42.
U.S. December crude fell $1.98 to settle at $86.67 a barrel, its lowest settlement since July 12. Tuesday's low trade was $85.69.
Tuesday's move lower left U.S. crude poised "for a test on the 61.8 percent retracement of the $77.28 to $100.42 move at $86.12, and possibly below," Michael Fitzpatrick, editor-in-chief, wrote in the industry newsletter EnergyOverview.
U.S. refined products futures extended multiday slides, with front-month RBOB gasoline futures off for a ninth straight session. They fell 4.25 cents to settle at $2.6050 a gallon, off 35.43 cents from its $2.9593 settlement on Oct. 10.
Front-month heating oil traded lower for the eighth straight session, dropping 3.33 cents to settle at $3.0434 a gallon, down 21.37 cents from Oct. 11 when it closed at $3.2571 a gallon.
Falling distillate inventories, especially in the U.S. Northeast, the country's biggest heating oil market, had stirred concerns about a potential fuel shortfall as winter approached.
But analysts said tepid demand for refined products and healthy crude oil inventories were weighing on gasoline and distillate prices.
"I think the judgment of the market is that, while (distillate) inventories are still low, they are likely to rise," said Tim Evans, energy analyst for Citi Futures Perspective in New York.
U.S. crude oil stocks rose 313,000 barrels last week, the American Petroleum Institute (API) said in a report late on Tuesday, a smaller build than expected.
Gasoline stocks rose 181,000 barrels and distillate stockpiles fell 890,000 barrels, the API said.
Crude stockpiles were expected to have risen 1.9 million barrels in the week to Oct. 19, according to analysts polled by Reuters.
Gasoline stocks were expected to be up 700,000 barrels, with distillate stocks seen down 900,000 barrels.
The government's report from U.S. Energy Information Administration (EIA) will follow on Wednesday at 10:30 a.m. EDT (1430 GMT).
The slide in crude prices on Tuesday came even as the potential remains for Middle East turmoil to disrupt the region's oil supply.
Iran said on Tuesday it would stop oil exports if pressure from Western sanctions got any tighter and that it had a "Plan B" contingency strategy to survive without oil revenues.
Major powers may ask Iran for stricter limits on its nuclear work if it wants an easing of harsh sanctions - a long-shot approach aimed at yielding a negotiated solution, according to Western diplomats.
Syrian rebels were attempting to seize an army base close to the main north-south highway, hoping to create a "safe zone" allowing them to focus on President Bashar al-Assad's southern strongholds. (Additional reporting by Matthew Robinson in New York, Peg Mackey in London and Manash Goswami in Singapore; Editing by Marguerita Choy, Alden Bentley, John Wallace and Jim Marshall)