To young people in Cambodia, who have no memory of Prince Sihanouk, Mr. Hun Sen represents modernity. Returning from Paris this month, he stepped off his airplane in a French double-breasted suit. He favors imported cigarettes and wears metal-frame glasses that help mask the scar from the shrapnel that took his left eye in 1975. Mr. Hun Sen takes advantage of his differences with the Prince while publicly urging him to come home. Meanwhile, he cleverly explains the Prince’s failure to do so by saying that the Prince remains allied to the Khmer Rouge, a relationship most Cambodians find disturbing. About his own experience with the Khmer Rouge, Mr. Hun Sen says little, and his official biography is mysterious. He says he joined the Khmer Rouge in 1970, after the coup that overthrew Prince Sihanouk, because the Prince himself had sided with them and had called for resistance to the American-backed Government of Lon Nol. But the Australian scholar Ben Kiernan, in his 1985 book, ”How Pol Pot Came to Power,” argues that Mr. Hun Sen was in contact with the Communists as early as 1967 when he fled the capital at 16 and worked as a courier for local Communist leaders before receiving military training.