NEW YORK (AP) _ Shares of Time Warner Inc. and America Online Inc. fell sharply Tuesday as investors grew more critical of the mammoth $145 billion corporate merger, worried that high-flying AOL could be bogged down by the job of integrating the slower-growing Time Warner.

Several financial analysts lowered their estimates of both companies amid concerns that AOL's growth could slow.

``You've got a new company that's going to grow at a lot slower pace than AOL was growing before,'' said Mike Wallace, an analyst with the Warburg Dillon Read securities firm.

The deal, initially worth $166 billion when announced Monday, has dropped $21 billion in value as investors have pushed AOL shares down.

AOL stock was down 11 percent in heavy trading on the New York Stock Exchange, dropping $8.25 a share to $64.37 1/2 at 5 p.m. EST. Time Warner stock was down 7 percent, falling $6.12 1/2 a share at $86.12 1/2.

Merrill Lynch & Co. estimated that AOL's stock could fall as low as $55 a share in the near term but also could rise as high as $90-$100 within a year, depending on how the merger goes and how well managers integrate the two companies.

``The difficulties, challenges, and risks involved, however, should not be ignored,'' Merrill Lynch analyst Henry Blodget said in the report released Tuesday.

Despite the concerns, most analysts remained confident about the deal, which helps both companies fill in gaps in their respective businesses.

AOL needs Time Warner's 13 million cable-TV lines to deliver the next generation of Internet technology to consumers: high-speed access that is up to 100 faster than through telephone lines.

Time Warner, for its part, gets a ready way to peddle its movies, magazines and television shows over the Internet.