Andover, Mass.--CMGI's Engage Technologies subsidiary announced Thursday it has agreed to buy online advertising network Adsmart, New York, and Flycast Communications Corp., San Francisco, for about $2.5 billion in stock. The move consolidates CMGI's holdings under the Engage corporate logo, and offers corporate advertisers access to ad placement for broad and specialized campaigns, as well as research, under one roof. Publishers will gain access to both banner advertising and cost-per-click advertising placement services. The transaction sets the stage for a battle royale between DoubleClick, New York, and Engage for dominance in the Internet advertising network market. Paul Schaut, Engage's president and CEO, will lead the combined companies.