* Nike declines after analyst downgrade
* Oil prices fall nearly 2 pct
* Dow up 0.1 pct, S&P up 0.1 pct, Nasdaq down 0.1 pct (Updates to close)
Aug 21 (Reuters) - The S&P 500 ended up slightly on Monday after two days of declines, though simmering tensions between the United States and North Korea kept investors on edge and a drop in oil prices weighed on energy shares.
Investors began to turn their focus to the Jackson Hole meeting of Federal Reserve Chair Janet Yellen and other global central bankers, due to start later this week.
Investors are angling for the slightest hint on where monetary policy is headed. Fed Vice Chair William Dudley, who has in the past taken a more dovish approach to policymaking, earlier this month said the fact that financial conditions have recently eased despite Fed rate increases is a reason to keep plans to tighten policy in place.
"That confluence of strong growth and low inflation, which is somewhat like nirvana for equity investors, we don't think can last forever," said Wayne Wicker, chief investment officer at ICMA-RC in Washington.
"We're hopefully getting a couple of more data points to see where the Fed takes their temperature on where they're feeling the economy is at this juncture so that we can anticipate if something happens in the fourth quarter or not."
The United States and South Korea began long-planned joint military exercises on Monday, heightening tensions with North Korea, which called the drills a "reckless" step toward nuclear conflict.
Tensions between the United States and North Korea and turmoil in the White House have caused stocks to sell off in the past two weeks.
Absent U.S. economic data or other headlines, "its a quiet Monday and people are still feeling the effects of last week. Now that earnings are over theres just not a whole lot of catalysts," said Ian Winer, head of equities at Wedbush Securities in Los Angeles.
Stock futures trading volume fell during the two hours that people left their offices to get a glimpse of the first total solar eclipse to unfold across the country in nearly a century.
About 174,000 S&P 500 e-mini futures futures changed hands in the two-hour period ending 3:30 p.m. E.T. on Monday, down about 46 percent from the comparable period last year.
The Dow Jones Industrial Average rose 29.24 points, or 0.13 percent, to 21,703.75, the S&P 500 gained 2.82 points, or 0.12 percent, to 2,428.37 and the Nasdaq Composite dropped 3.40 points, or 0.05 percent, to 6,213.13.
The S&P 500 energy index was down 0.6 percent, leading sector declines in the S&P 500, after crude oil prices fell nearly 2 percent, pulling back from last week's rally.
While the benchmark S&P 500 index is still up 13.5 percent since the election, it had fallen 2.1 percent in the last two weeks. That's the most since the two weeks before the election.
The Dow ended above its 50-day moving average after briefly falling below it during the session, while the S&P 500 remained below the 50-day technical level.
Shares of sporting good retailers took a hit after analysts downgraded ratings on Nike, Foot Locker and other companies. Nike's shares fell 2.4 percent, while Foot Locker shares slid 7.4 percent.
Johnson Controls rose 3.3 percent to $38.27, among the top S&P 500 gainers, after saying its CEO change would happen earlier than announced.
Herbalife surged 9.8 percent after the nutritional supplement maker said it would buy back $600 million of shares after ending talks to be taken private.
Declining issues outnumbered advancing ones on the NYSE by a 1.01-to-1 ratio; on the Nasdaq, a 1.30-to-1 ratio favored decliners. (Additional reporting by Dion Rabouin in New York and Sruthi Shankar in Bengaluru; Editing by Nick Zieminski and Steve Orlofsky)