TECHNOLOGY & TELECOMMUNICATIONS

Petaluma-based Advanced Fibre Communications Inc. shares plunged 52% after the maker of equipment used to boost capacity of phone networks warned of lower second-quarter earnings because it lost a contract with GTE Corp., its largest customer. Advanced Fibre stock fell $20.94 to close at $19.13 in Nasdaq trading. Advanced Fibre said it expects the lost contract and its problems in China to reduce second-quarter profit to 7 cents to 9 cents a share, about half the 17-cent estimate of analysts. GTE was Advanced Fibre’s largest customer in 1997, accounting for 20% of the company’s $267.9 million in sales. GTE chose Advanced rivals DSC Communications Corp., Reltec Corp. and Northern Telecom Ltd.