* Utilities sector S&P's biggest gainer after weekly decline
* Caterpillar at record high after brokerage upgrade
* Nasdaq biotech index has worst day since mid-December
* GoPro pares losses on sale talk after plunging on warning
* Dow down 0.05 pct, S&P up 0.17 pct, Nasdaq up 0.29 pct (Updates to close, adds commentary)
Jan 8 (Reuters) - The S&P 500 extended its winning streak for 2018 on Monday although its advance slowed to a crawl as the healthcare and financial sectors weighed and investors awaited the start of the quarterly earnings season.
The healthcare sector was the S&P's worst performer on Monday, and investors were cautious about pouring money into bank stocks before the companies kick off the fourth-quarter earnings season later this week.
"We had a big move last week and everyone knows earnings is coming up. People don't want to chase too much further when you have a round of fundamental inputs in the next few weeks," said Michael ORourke, chief market strategist at JonesTrading in Greenwich, Connecticut.
The Dow Jones Industrial Average fell 12.87 points, or 0.05 percent, to 25,283, the S&P 500 gained 4.56 points, or 0.17 percent, to 2,747.71, and the Nasdaq Composite added 20.83 points, or 0.29 percent, to 7,157.39.
The three major indexes kicked off 2018 with their strongest first four trading days in more than a decade, according to Reuters data. The Dow had its strongest start since 2003, and the Nasdaq and S&P 500 had their strongest starts since 2006.
Historically, the first five trading days of January can be an indicator for the market's direction for the full year, according to the Stock Traders Almanac.
The S&P 500's healthcare sector ended 0.4 percent lower. Last week it rose 3.2 percent.
The Nasdaq biotech index fell 1.4 percent, on track for its biggest one-day percentage decline since mid-December, led by a 3.7 percent drop in Biogen Inc and a 3.3 percent decline in Regeneron Pharmaceuticals Inc.
A 0.4 percent decline in the bank subsector pressured the broader financials index, which fell 0.1 percent. Investors were waiting for more details about the impact of recent U.S. corporate tax cuts in fourth-quarter earnings calls when the reporting season begins later in the week.
Wells Fargo and Citigroup fell more than 1 percent while Goldman Sachs declined 1.5 percent. Most big U.S. lenders have estimated one-off charges to their fourth-quarter earnings on account of U.S. tax cuts.
Utilities were the S&P's biggest percentage gainers, regaining some ground lost in the previous week along with real estate.
Caterpillar closed up 2.5 percent to $166.03, just below a record high set earlier in the day, after JP Morgan upgraded the stock saying the tax overhaul could help North America's construction business cycle extend in 2018.
Kohl's Corp rose 4.7 percent after the department store operator posted far stronger same-store sales for the holidays than its bigger peers.
GoPro Inc shares ended down 12.8 percent at $6.56 after the company said it would be open to a sale but is not actively pursuing one. Earlier in the day, the shares lost about a third of their value, hitting a record low at $5.04, after GoPro announced preliminary fourth-quarter revenue that was well below expectations and said it would exit the drone business.
Advancing issues outnumbered declining ones on the NYSE by a 1.40-to-1 ratio; on Nasdaq, a 1.03-to-1 ratio favored advancers.
The S&P 500 posted 98 new 52-week highs and no new lows; the Nasdaq Composite recorded 124 new highs and 26 new lows.
Volume so far on U.S. exchanges was 6.36 billion shares, compared to the 6.28 billion average for the full session over the last 20 trading days. (Additional reporting by Sruthi Shankar in Bengaluru; Editing by Nick Zieminski and Leslie Adler)