* AstraZeneca rejects sweetened Pfizer offer
* AT&T to buy DirecTV for $48.5 billion
* Futures off: Dow 42 pts, S&P 4 pts, Nasdaq 6.5 pts (Adds Campbell Soup earnings, updates prices)
By Chuck Mikolajczak
NEW YORK, May 19 (Reuters) - U.S. stocks were set to dip at the open on Monday, on the heels of back-to-back weekly declines for the S&P 500 as investors grew cautious over stock valuations with indexes near record levels amid mixed economic data.
* U.S. listed shares of AstraZeneca slumped 8.8 percent to $73.20 in premarket trade after 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 1.7 percent to $29.60 before the opening bell.
* AT&T lost 2.5 percent to $35.83 in premarket trade after the telecom company said it will acquire DirecTV for $48.5 billion, highlighting AT&T's pressing need for fresh avenues of growth beyond the maturing U.S. cellular business. DirecTV shares lost one cent at $86.17 in premarket.
* Equities have come under pressure recently, with consecutive weekly declines for the first time since January as investors have become leery of growth prospects as a result of mixed economic data.
* Small-cap stocks, often seen as the first beneficiary of growth, have tumbled. The small-cap Russell 2000 index has several times approached correction territory, defined as a decline of 10 percent from a recent high, only to bounce back slightly.
* The defensive posture by investors has been reflected by a sector rotation into groups such as utilities, telecoms and energy, which have outperformed the broader S&P 500 over the past three months.
* S&P 500 e-mini futures lost 4 points and were slightly below fair value, a formula that evaluates pricing by taking into account interest rates, dividends and time to expiration on the contract. Dow Jones industrial average e-mini futures declined 42 points and Nasdaq 100 e-mini futures lost 6.5 points.
* Campbell Soup Co fell 4.8 percent to $42.95 in premarket after 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 the 464 companies in the S&P 500 that have reported earnings 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)