International relief agencies began to restore vital services in the Cook Islands and provide aid to those left homeless by a hurricane that Prime Minister Tom Davis called the worst ever to hit that South Pacific island chain. Davis said the islands' economy was set back several years by Hurricane Sally, which struck Saturday with 90-m.p.h. winds and 30-foot waves. No casualties were reported, but damage was estimated at $25 million. He said 1,000 people were left homeless on the largest island, Rarotonga. The Cook Islands is a self-governing territory in free association with New Zealand.