San Francisco--CNET, an online technology portal, announced Thursday the launch of its first major advertising campaign, a $100 million, multimedia push scheduled to unfold over the next 18 months. CNET is vying with ZDNet for tech portal supremacy on the Web. ZDNet currently promotes its suite of tech sites in Ziff-Davis magazines and on ZDTV. CNET had 8.2 million visitors in May, according to the latest MediaMetrix figures. The ZDNet sites had 7.8 million visitors. The ad campaign is designed to increase CNET's slim advantage. Using the tagline ``The source for computers and technology,'' the campaign will begin with its print component, which will appear in daily newspapers and business, information technology and tech-enthusiast magazines. The humorous radio and TV spots attempt to show the value of CNET as an unbiased source for tech product reviews. Citron Haligman Bedecarre Euro RSCG, San Francisco, created the campaign.