* Producer prices fall in February
* UMich edges lower in March
* General Mills falls after outlook
* Aeropostale drops after earnings
* Indexes off: Dow 0.17 pct, S&P 0.22 pct, Nasdaq 0.39 pct
By Chuck Mikolajczak
NEW YORK, March 14 (Reuters) - U.S. stocks were down modestly on Friday, keeping the S&P below a key support level for a second day, with investors reluctant to make big bets ahead of a referendum in Crimea this weekend.
U.S. Secretary of State John Kerry will seek assurances from Russia on Friday that it will not seek to annex Crimea and will address concerns over Ukraine through negotiation, a senior State Department official said before talks in London.
Kerry's meeting is an attempt to defuse tension between Moscow and the West ahead of the referendum, which looks set to proceed on Sunday, that will decide whether Crimea, a Russian-majority region of Ukraine, will become part of Russia.
"There is a lot of anticipation about that Crimea vote coming up, so that is out there, a little bit of uncertainty," said Ryan Detrick, senior technical strategist at Schaeffer's Investment Research in Cincinnati, Ohio.
Russia's navy said fighter jets had started training exercises over the Mediterranean Sea, an announcement likely to raise tensions in the standoff with Ukraine.
The S&P 500 suffered its worst decline since early February on Thursday, sending the benchmark index below a key technical support level at 1,850.
"That 1,850 level on the S&P is the area we didn't want to see violated and obviously that big round number did," said Detrick.
Producer prices fell 0.1 percent in February, dragged down by falling costs for services, offering little sign of inflation pressures.
The preliminary Thomson Reuters/University of Michigan overall index of consumer sentiment fell to 79.9 in March, down from the 81.6 final reading in February, entirely due to reduced expectations for the future.
The Dow Jones industrial average fell 26.94 points or 0.17 percent, to 16,081.95, the S&P 500 lost 3.98 points or 0.22 percent, to 1,842.36 and the Nasdaq Composite dropped 16.46 points or 0.39 percent, to 4,243.96.
General Mills Inc fell 2 percent to $49.99 after it warned third-quarter earnings would fall below analysts' expectations as it faces increased competition from store brands and spends more on marketing its yogurts.
General Motors Co gained 1.4 percent to $34.26. The automaker is facing increasing pressure to compensate victims for an ignition defect that prompted the recall of 1.6 million vehicles.
Cooper Tire & Rubber Co jumped 6.3 percent to $24.25 after reporting fourth-quarter earnings.
Aeropostale Inc tumbled 14.4 percent to $6.25 after the teen apparel retailer reported its fifth straight quarterly loss.