* Dollar weakens, supporting crude prices
* Gilead Pharma shares fall, biotech index down
* Indexes: Dow up 0.14 pct, S&P up 0.06 pct, Nasdaq off 0.13 pct (Updates prices, comment)
By Rodrigo Campos
NEW YORK, March 23 (Reuters) - U.S. stocks were little changed on Monday, following strong gains in major indexes the previous week, as investors assessed gyrations in the dollar and crude prices and their impact on equities.
Gains expanded and contracted, tracking the behavior of energy stocks as crude oil prices were caught between the weakness in the U.S. dollar and concerns about oversupply. The S&P 500 energy sector rose 0.2 percent after earlier gaining as much as 0.9 percent.
The action in the dollar has closely affected stocks of late as traders focus on the Federal Reserve and its expected monetary policy tightening sometime later this year. The 20-day correlation between the dollar index and the S&P 500 sits at -0.79. The dollar index was down 0.8 percent on the day.
"The market has been in a back-and-forth motion for the last couple of weeks, caught between the potential for rising interest rates and its impact on the dollar and the feeling by investors that the economy is gaining some strength," said Rick Meckler, president of LibertyView Capital Management in Jersey City, New Jersey.
"Oil is confusing for investors," he said. Its decline "puts more money in the pocket of consumers, but the drop has been so precipitous it creates problems for a large part of the market."
At 12:18 p.m. EDT (1618 GMT) the Dow Jones industrial average rose 25.46 points, or 0.14 percent, to 18,153.11, the S&P 500 gained 1.16 points, or 0.06 percent, to 2,109.26 and the Nasdaq Composite dropped 6.32 points, or 0.13 percent, to 5,020.10.
Brent was recently up 0.2 percent, while U.S. crude added 0.4 percent even after top exporter Saudi Arabia said it would only mull cutting output if producers outside OPEC do so as well.
Kansas City Southern shares fell 7.7 percent to $106.71 after the railroad cut its full year revenue forecast to "low-single digit" percentage growth from "mid-single digit" due to lower carload growth, primarily from the energy sector.
Gilead Sciences shares fell 2 percent to $100.21 after a Bloomberg report said the company told healthcare providers nine patients taking its hepatitis C drugs along with a heart treatment developed abnormally slow heartbeats and one died of cardiac arrest.
Immunogen rallied 17.2 percent to $8.72 after it licensed Japan-based Takeda Pharmaceutical to develop and commercialize anticancer therapies.
The Nasdaq Biotech index fell for the first time in nine sessions, down 1.9 percent, after running up nearly 20 percent from its February low.
Advancing issues outnumbered declining ones on the NYSE by 1,875 to 1,070, for a 1.75-to-1 ratio; on the Nasdaq, 1,467 issues rose and 1,169 fell for a 1.25-to-1 ratio favoring advancers.
The S&P 500 index was posting 58 new 52-week highs and 1 new low; the Nasdaq Composite was recording 111 new highs and 28 new lows.
(Editing by Bernadette Baum and Nick Zieminski)