President Leopold Sedar Senghor formally resigned as head of state of Senegal , the west African country he has led since its independence from France 20 years ago. Mr. Senghor will be succeeded by Abdou Diouf, who has been his prime minister for the past 10 years. The poet-president earlier this month made known his decision to retire. His announced decision, without a close parallel in Africa's modern history, could be seen as intended to set an example for other elder statesmen on the continent. Political sources in Dakar said Mr. Diouf's choice of prime minister would be a nonpolitical one to avoid fueling opposition criticism about the handover of power.