New York ? Increasingly despondent investors sent stocks falling again Monday, as poor earnings outlooks and concerns about the economy eclipsed a pair of multibillion-dollar mergers. The Nasdaq composite index and Standard & Poor’s 500 both closed at new lows for 2004.

Health care and pharmaceutical stocks rose as Mylan Laboratories Inc. made a $4 billion all-stock offer for King Pharmaceuticals Inc. Financial stocks also moved slightly higher as Spanish bank Banco Santander offered $15.3 billion for British mortgage lender Abbey National.

Trading on Wall Street remained lackluster, however, as investors awaited earnings reports later in the week from Aetna Inc., Boeing Co., Exxon Mobil Corp., Time Warner Inc. and Verizon Communications Inc.

Even more importantly, investors were waiting for more economic data to help determine whether the economy’s slowdown in June was transitory — or a sign of things to come.

“This is much more than the usual summer doldrums. There’s a message coming from the market, here,” said Hugh Johnson, chief investment officer at First Albany Corp. “If I were to simplify that message, it’s that the economy and earnings in the third and fourth quarter won’t be as strong as we expected.”

The Dow Jones industrial average fell 0.30, or nearly flat, at 9,961.92, after having been moderately lower for much of the session. Broader stock indicators also were lower. The Standard & Poor’s 500 index was down 2.13, or 0.2 percent, at 1,084.07, its lowest close since Dec. 17. The Nasdaq composite index shed 10.07, or 0.5 percent, to 1,839.02, its lowest point since Oct. 2.

With more than half the companies that make up the S&P 500 reporting earnings so far, more than two-thirds have exceeded estimates for second-quarter earnings. But the strong profits have been overshadowed by lower outlooks for the rest of the year from a number of major corporations.