|Man carries wreath of flowers outside Monaco's cathedral|
Those in attendance will include President Jacques Chirac of France and King Juan Carlos of Spain.
Former Navy Secretary John Lehman and U.S. Ambassador to France Howard Leach will represent the United States.
The prince passed away on April 6, almost one month after his hospitalization for heart, kidney and breathing problems.
He assumed the throne in 1949 and helped turn the tiny city-state on the French Riviera from an obscure town to a major financial center - famous for casinos and auto races.
His 1956 marriage to American movie star Grace Kelly brought great publicity to Monaco. She died in a car crash in 1982.
Prince Albert, Rainier's 47-year-old son, is Monaco's new ruler.
Some information for this report provided by AFP and Reuters.