* Existing home sales hit 9-month low
* Goldman cuts Boeing to sell rating
* Valeant, Salix agree to merger
* Indexes off: Dow 0.27 pct, S&P 0.22 pct, Nasdaq 0.06 pct (Updates to midday)
By Caroline Valetkevitch
NEW YORK, Feb 23 (Reuters) - U.S. stocks were down slightly in midday trading Monday as lower oil prices dragged down energy shares, pulling the Dow and S&P 500 off recent record levels.
Oil prices fell, with WTI crude off $1.30 at $49.50 a barrel on oversupply concerns and a stronger dollar, pushing the S&P energy index down 0.6 percent.
Housing stocks lost ground, with the PHLX housing sector index off 0.7 percent after existing home sales fell sharply to their lowest in nine months in January.
Investors were also reluctant to make big bets before Federal Reserve Chair Janet Yellen's semiannual testimony this week on the economy and monetary policy before the Senate Banking Committee, which will be closely watched for any indications on the timing of an interest rate hike.
A conditional agreement by euro zone finance ministers to extend Greece's bailout sent the Dow and S&P to record levels late last week, while the Nasdaq moved closer to its all-time high from March 2000.
"Crude continues to be very weak. But you can argue that as long as it stabilizes and doesn't completely plunge it's probably a positive, so it's really going to depend on earnings and macro news in the market right now," said Uri Landesman, president of Platinum Partners in New York.
At 12:53 p.m., the Dow Jones industrial average fell 49.8 points, or 0.27 percent, to 18,090.64, the S&P 500 lost 4.56 points, or 0.22 percent, to 2,105.74 and the Nasdaq Composite dropped 2.81 points, or 0.06 percent, to 4,953.16.
Boeing fell 2.5 percent to $154.10 as the biggest drag on the Dow after Goldman Sachs cut its rating on the aircraft maker to "sell" from "neutral."
Canada's Valeant Pharmaceuticals International Inc agreed to acquire gastrointestinal drugmaker Salix Pharmaceuticals Ltd in an all-cash deal valued at about $10.1 billion, the companies said on Sunday. U.S. listed shares of Valeant gained 13.2 percent to $196.14 while Salix slipped 1.1 percent to $156.06.
Declining issues outnumbered advancing ones on the NYSE by 1,709 to 1,277, for a 1.34-to-1 ratio; on the Nasdaq, 1,611 issues fell and 1,035 advanced, a 1.56-to-1 ratio.
The S&P 500 was posting 62 new 52-week highs and one new low; the Nasdaq Composite was recording 102 new highs and 30 new lows. (Editing by Bernadette Baum and Nick Zieminski)