* Nike shares surge after results, Amazon program
* Nasdaq dips as biotechs decline
* S&P tech sector posts first monthly loss of year
* Dow up 0.29 pct, S&P up 0.15 pct, Nasdaq down 0.06 pct (Updates to close of U.S. markets)
By Lewis Krauskopf
June 30 (Reuters) - Major U.S. stock indexes on Friday ended a volatile week on a modestly high note, boosted by Nike's well-received quarterly report, with the S&P 500 tallying its best first half of the year since 2013.
Nike shares rose 11 percent after the world's largest footwear maker reported a quarterly profit that topped estimates and said it would launch a pilot online sales program with Amazon.com. Nike shares gave the biggest boost to the Dow industrials and the S&P 500.
The S&P technology index ended down 0.1 percent and posted its first monthly loss of the year, while a decline in biotech shares, which had surged of late, also limited the Nasdaq.
Tech has led the S&P 500's 8.2 percent rally this year, but its recent pullback suggests investors may be cashing in those profits to rotate to other sectors.
"Are we going to see a broadening of the rally, where you see more of the financials and other sectors fill in some of the gaps?" said Alan Lancz, president of Alan B. Lancz & Associates Inc., an investment advisory firm in Toledo, Ohio.
"It hasn’t been a broad encompassing rally that I think investors will have to see a little bit more conviction rather than just in a handful of stocks," Lancz said.
The Dow Jones Industrial Average rose 62.6 points, or 0.29 percent, to 21,349.63, the S&P 500 gained 3.71 points, or 0.15 percent, to 2,423.41 and the Nasdaq Composite dropped 3.93 points, or 0.06 percent, to 6,140.42.
Industrials were the top performing sector, rising 0.8 percent.
"When you look at some of the stocks that are doing particularly well today, they are some of those economically sensitive-type stocks," said Chuck Carlson, chief executive officer at Horizon Investment Services in Hammond, Indiana.
"During a time when it seems like there are still a fair amount of naysayers out there about the economy and GDP, anytime you get some of those stocks showing some strength, it probably emboldens the market,” Carlson said.
With the second quarter coming to a close, the S&P 500 recorded its biggest percentage first-half gain since climbing 12.6 percent in the first six months of 2013. The Nasdaq posted its biggest first-half gain since 2009.
U.S. consumer spending rose modestly in May and inflation cooled, pointing to a slow-but-steady economic expansion. The Commerce Department data bolstered the view that the U.S. economy is rebounding in the second quarter.
Investors have been concerned about recent mixed economic data at a time that the Federal Reserve begins lifting interest rates from very low levels.
Second-quarter corporate results are set to begin in earnest in the coming weeks, with S&P 500 companies expected to post an 8-percent rise in earnings, according to Thomson Reuters I/B/E/S.
Investors have been looking for earnings to support historically high valuations, with the S&P 500 trading at about 18 times earnings estimates for the next 12 months compared to the long-term average of 15 times.
"We can talk about the economy and geopolitical risk but earnings drive the market," said Chris Bertelsen, chief investment officer of Aviance Capital Management in Sarasota, Florida. "We’re bumping right along the top end of" historic valuation levels.
About 6.6 billion shares changed hands in U.S. exchanges, below the 7.3 billion daily average over the last 20 sessions.
Advancing issues outnumbered declining ones on the NYSE by a 1.60-to-1 ratio; on Nasdaq, a 1.01-to-1 ratio favored decliners.
Additional reporting by Kimberly Chin in New York and Ankur Banerjee, Anya George Tharakan and Tanya Agrawal in Bengaluru; Editing by Arun Koyyur and Nick Zieminski