* Futures down: Dow 109 pts, S&P 12.5 pts, Nasdaq 35 pts
By Yashaswini Swamynathan
Sept 12 (Reuters) - U.S. stock index futures were lower for the third straight day on Monday as oil prices fell and on increasing speculation about a possible U.S. interest rate hike as early as next week.
* Even as the Federal Reserve has given little indication on the timing of the next rate hike, investors have taken cues from a number of top central bank officials hinting at a possible raise at the Fed's next policy-setting meeting on Sept. 20-21.
* Fed Governor and permanent voting member Lael Brainard's speech at 1:15 p.m. ET (1715) will be scrutinized to see if she maintains her dovish stance on rates or takes a more aggressive posture. Her speech was announced on Friday.
* Other Fed members including Minneapolis Fed President Neel Kashkari and his Atlanta counterpart Dennis Lockhart are scheduled to speak at separate events. Both are non-voting members. Lockhart has said he expects two rates this year.
* Low expectations for an interest rate hike this year had partly helped the benchmark S&P 500 index clock a series of record highs since July.
* However, on Friday, the three major U.S. stock indexes saw their worst decline since the Brexit vote in June, as growing evidence of an imminent rate hike spooked investors away from riskier parts of the markets.
* Such prospect pushed the dollar index slightly higher on Monday, marking the fourth straight day of gains, while oil prices tumbled nearly 2 percent also amid worries of oversupply.
* September tends to be a month of lower returns for stocks, and traders said this year could be no exception given the abundance of uncertainties including the rate outlook and November's U.S. election.
* Democratic U.S. presidential candidate, Hillary Clinton's illness added another layer of uncertainty in the markets in the final weeks before the November elections.
* Shares of technology stocks, including Apple, Alphabet, Facebook and Yahoo were down more than 1 percent in premarket trading.
* Perrigo rose 3 percent after activist investor Starboard Value disclosed a 4.6 percent stake and delivered a letter to the drugmaker's executives.
Futures snapshot at 7:05 a.m. ET:
* Dow e-minis were down 109 points, or 0.6 percent, with 15,733 contracts changing hands.
* S&P 500 e-minis were down 12.5 points, or 0.59 percent, with 198,982 contracts traded.
* Nasdaq 100 e-minis were down 35 points, or 0.75 percent, on volume of 16,955 contracts. (Reporting by Yashaswini Swamynathan in Bengaluru; Editing by Savio D'Souza)