* AstraZeneca rejects sweetened Pfizer offer
* AT&T to buy DirecTV for $48.5 billion
* Indexes: Dow off 0.05 pct, S&P up 0.11 pct, Nasdaq up 0.46 pct (Updates to market open, adds quote)
By Chuck Mikolajczak
NEW YORK, May 19 (Reuters) - U.S. stocks were little changed on Monday, on the heels of back-to-back weekly declines for the S&P 500, as investors exercised caution over valuations after a run of mixed economic data.
U.S.-listed shares of AstraZeneca slumped 9.6 percent to $72.60. The British drugmaker rejected a sweetened and "final" merger offer from Pfizer which would have created the world's largest pharmaceuticals group. Pfizer shares advanced 1.5 percent to $29.56.
AT&T lost 1.7 percent to $36.12 after the telecom company said it will acquire DirecTV for $48.5 billion, as it seeks fresh avenues of growth beyond the maturing U.S. cellular business. DirecTV shares lost $1.81 at $84.37.
Equities have come under pressure, with consecutive weekly declines for the first time since January, as investors have become leery about growth prospects. Last week, readings on retail sales and consumer sentiment fell shy of expectations while labor and housing data provided reason for optimism.
"The issues really are more the U.S. economy and the fact equity investors are very hopeful we will see an acceleration in the economy," said Tim Ghriskey, chief investment officer of Solaris Group in Bedford Hills, New York.
"We still get very mixed economic signals - one positive data point is in contrast with a negative data point."
Small-cap stocks, often the first beneficiaries of growth, have tumbled. The small-cap Russell 2000 index has several times approached correction territory, a decline of 10 percent from a recent high, only to bounce back slightly.
Investors' defensive posture has been reflected by a sector rotation into utilities, telecoms and energy, which have outperformed the broader S&P 500 over the past three months.
The Dow Jones industrial average fell 7.7 points or 0.05 percent, to 16,483.61, the S&P 500 gained 2.14 points or 0.11 percent, to 1,880 and the Nasdaq Composite added 18.74 points or 0.46 percent, to 4,109.33.
Campbell Soup Co fell 3.4 percent to $43.58, the worst performer on the S&P 500. The world's largest soup maker posted weaker-than-expected quarterly sales and cut its full-year sales guidance.
Earnings season will effectively draw to a close this week, with 23 companies scheduled to report, including retailers Home Depot and Lowe's Cos.
Of 464 S&P 500 companies that reported through Friday, 69.2 percent beat expectations, above the long-term average of 63 percent and the 66 percent average over the past four quarters. (Editing by Bernadette Baum and Nick Zieminski)