* Futures down: Dow 233 pts, S&P 29 pts, Nasdaq 77 pts
By Tanya Agrawal
Sept 22 (Reuters) - U.S. stock index futures were down about 1.5 percent on Tuesday as oil and copper prices fell on uncertain demand from China.
* Copper prices hit two-week lows, while oil was down about 2 percent. Chinese government efforts to stimulate growth by easing fiscal and monetary policy have yet to bear fruit.
* U.S. stocks ended higher on Monday, rebounding from losses late last week with help from Apple and financial shares, but a drop in biotech shares limited the advance.
* Investors are also looking for more clarity from the Federal Reserve after its decision last week to hold interest rates at near-zero levels.
* Fears of slowing growth in China sparked a sharp selloff in global stock markets in recent weeks and the Fed's comments about the global economy exacerbated those concerns.
* Atlanta Fed President Dennis Lockhart said on Monday a rate hike later this year was still possible and that the Fed, in recent months, has added to the market instability and needs to refine its communication approach.
* The dollar hit an almost two-week high against a basket of currencies on Tuesday after the comments from Lockhart, a voting member of the Federal Open Market Committee. He is scheduled to speak later in the day.
* Particular attention will be paid to Chair Janet Yellen's speech on Thursday at the University of Massachusetts Amherst.
* Shares of Bank of America were down 1.7 percent at $15.44 premarket ahead of a shareholder vote on separating the bank's chief executive and chairman roles.
* Freeport McMoRan was down 4 percent at $10.11 as the miner and energy producer was hit by falling commodity prices.
* Biotech companies were down for a second day after U.S. Democratic presidential candidate Hillary Clinton said she would announce a plan to stop "price gouging" for specialty drugs. Gilead fell 1.2 percent and Biogen fell 2 percent.
Futures snapshot at 6:58 a.m. ET (1058 GMT):
* S&P 500 e-minis were down 28.75 points, or 1.46 percent, with 251,193 contracts traded.
* Nasdaq 100 e-minis were down 77 points, or 1.77 percent, on volume of 49,059 contracts.
* Dow e-minis were down 233 points, or 1.42 percent, with 38,305 contracts changing hands. (Reporting by Tanya Agrawal in Bengaluru; Editing by Savio D'Souza)