* Major indexes on track for strong weekly gains
* U.S. and Russia engage in tit-for-tat sanctions
* Nike shares fall in premarket after outlook
* Futures up: Dow 36 pts, S&P 4.6 pts, Nasdaq 9.5 pts
By Ryan Vlastelica
NEW YORK, March 21 (Reuters) - U.S. stock index futures edged higher on Friday, with major indexes on track for a week of strong gains, though geopolitical concerns remained in view as the tenuous situation in Ukraine continued.
* The biggest East-West confrontation since the Cold War ramped up after U.S. President Barack Obama targeted some of Russian President Vladimir Putin's closest long-time political and business allies in response to Russia's seizure of Crimea from Ukraine. Russia retaliated with sanctions of its own against top U.S. politicians.
* With the S&P 500 within 1 percent of record levels, some analysts say equities are vulnerable to any fallout from escalating geopolitical tensions, even though few U.S. companies have substantial exposure to the region. Still, stocks have moved sharply higher this week, boosted by Moscow's assertion that no other Ukrainian region would be subject to intervention.
* In another facet of emerging market concerns, Nike Inc late Thursday said growing pressures from weaker emerging market currencies would take a big toll on its profit in the current quarter. The athletic apparel maker, which gets about 30 percent of its revenue from emerging markets, also said China sales would be unchanged or slightly down this quarter. Shares fell 2.9 percent to $77 in light premarket trading.
* S&P 500 futures rose 4.6 points and were above fair value, a formula that evaluates pricing by taking into account interest rates, dividends and time to expiration on the contract. Dow Jones industrial average futures rose 36 points and Nasdaq 100 futures rose 9.5 points.
* For the week, the Dow, S&P and Nasdaq are all up 1.7 percent.
* Despite the recent strength, volume has been anemic on positive market days, suggesting limited conviction behind the move. However, volume is expected to surge on Friday as options expiration takes place alongside multiple index rebalances. Credit Suisse estimates $14 billion in gross trading will stem from the S&P 500 index rebalance, with another $6 billion coming from rebalancing in other indexes.
* WellPoint Inc raised its earnings outlook, saying it expected strong membership growth.
* In earnings news, Tiffany & Co reported adjusted fourth-quarter earnings that missed expectations, while Darden Restaurants Inc reported third-quarter revenue that was slightly below forecasts.
* The U.S. Federal Reserve late Thursday said that big U.S. banks have enough capital buffers to withstand a drastic economic downturn. The central bank said 29 out of 30 major banks met the minimum hurdle in its annual health check. The only bank to fall under the 5 percent requirement for top-tier capital was Zion Bancorp, which said it would resubmit a capital plan to the Fed. (Editing by Chizu Nomiyama)