AT&T shares fell yesterday after the chairman, Mr Robert Allen, said the telecommunications group's third-quarter earnings would be as much as 10 per cent below the average forecast by analysts. Shares tumbled $5.12 (8.9 per cent) to $52.12 on Wall Street. The sharp decline also hurt rivals such as MCI, whose shares fell 94 cents to $26.18 and Sprint, off $1.12 to $40.37. Mr Allen said AT&T earnings would be well below the average per-share estimate of 92 cents, due largely to fierce competition in the long-distance telephone market.