First-quarter advertising spending grew 4.6% to $19.1 billion, up from about $18.3 billion during the first three months of 1998, according to Competitive Media Reporting, an advertising tracking firm. General Motors Corp. was the biggest advertiser, spending $622.7 million in the quarter, up 16.4% from the same period in 1998. Procter & Gamble Co. was the second-largest advertiser, spending $393 million. Automobile giant DaimlerChrysler was third with $340.4 million in total spending. On the soft-drink front, PepsiCo spent $65.4 million in the first quarter, surpassing Coca-Cola Co. for the first time since 1990. Coke spent $58.4 million. Keeping with recent trends, the fastest-growing category in the quarter was Internet services, followed by prescription drugs.