* Nike down after revenue misses estimates
* S&P 500 slips back to negative turf for 2016
* All three indexes down 2 pct (Updates to open)
By Abhiram Nandakumar
March 23 (Reuters) - U.S. stock indexes were slightly lower on Wednesday morning, dragged down by energy and materials stocks, as investors remained wary of taking on risk in a week marred by the attacks in Brussels and shortened by the Good Friday holiday.
Oil prices were lower after data showing a rise in U.S. stockpiles last week rekindled worries about a global glut. Gold and metals prices also fell as the dollar strengthened on hawkish comments from U.S. Federal Reserve policymakers.
The Dow Jones industrial average held onto meager gains for the year after a five-week rally helped the market recover from a steep selloff at the start of the year. The S&P 500 slipped back to negative territory for 2016.
"We've seen a tremendous run-up largely related to the fact that the world didn't end after all, but it is hard to see where we get the kind of improvement from here which would drive the market sustainably higher," said Brad McMillan, chief investment officer at Commonwealth Financial Network in Waltham, Massachusetts.
At 9:39 a.m. ET, the Dow Jones industrial average was down 35.16 points, or 0.2 percent, at 17,547.41, the S&P 500 was down 4.18 points, or 0.2 percent, at 2,045.62 and the Nasdaq Composite was down 9.62 points, or 0.2 percent, at 4,812.04.
Nine of the 10 major S&P sectors were lower, led by the 0.85 percent fall in the materials sector. Newmont Mining shares were down 4.7 percent at $26.09 and weighed the most on the sector.
Energy stocks were off 0.73 percent, with Chevron's 0.8 percent decline exerting the biggest influence.
Investors were assessing recent comments from Fed officials, supporting more interest rate hikes this year as the economy continues to show signs of resilience.
Data on Wednesday includes single-family home sales for February, due at 10 a.m. (1400 GMT). Sales are expected to have risen 3.2 percent, suggesting that the housing market continues to recover.
Nike shares were down 4.8 percent at $61.80 after the world's largest footwear maker reported quarterly revenue below estimates. The stock was the biggest drag on the Dow.
Gilead Sciences was down 2 percent at $91.87 after a federal jury upheld the validity of two Merck patents in a high-profile dispute over Gilead's blockbuster cure for hepatitis C. Merck was up half a percent.
Valeant Pharmaceuticals was up 2.6 percent at $32.72, set for a third-straight day of gains.
Michaels Cos was down 2.7 percent at $26.20 after private equity sponsors cut their stakes further in the arts and crafts retailer.
Declining issues outnumbered advancing ones on the NYSE by 1,831 to 716. On the Nasdaq, 1,426 issues fell and 769 advanced.
The S&P 500 index showed three new 52-week highs and no new lows, while the Nasdaq recorded 10 new highs and seven new lows. (Reporting by Abhiram Nandakumar in Bengaluru; Editing by Ted Kerr and Don Sebastian)