SINGAPORE, NOV. 26 -- After 31 years in office, Prime Minister Lee Kuan Yew today submitted his resignation in favor of a hand-picked successor in a move he has described as a "changing of the guard" to allow a younger generation of leaders to take over.

Lee, whose tenure makes him the world's longest-serving prime minister, formally announced his resignation, effective Wednesday, in a letter to Singapore's ceremonial president, Wee Kim Wee.

"I hereby tender my resignation and that of my government," the letter said. It called on Wee to ask Lee's chosen successor, First Deputy Prime Minister Goh Chok Tong, to form a new government to lead this prosperous island state of 2.7 million people.

Lee, who has been the only prime minister independent Singapore has known, has been planning his resignation for months and is expected to retain much power. As a result, today's announcement sparked little reaction here.

The 67-year-old Lee has said he plans to remain in the cabinet as a "senior minister without portfolio" and continue to head the ruling People's Action Party, which holds a virtual monopoly on political power. There also has been speculation that he might run for president after that office is given greater authority under legislation currently before Parliament.

While acknowledging that Lee will remain a dominant figure in Singapore's politics, government officials forecast a more relaxed, less autocratic leadership style under the 49-year-old Goh. He has said he favors more emphasis on consensus-building and consultation.

Lee, who assumed the premiership of this former British colony in 1959 and led Singapore to full independence in 1965, has been perceived as grooming his son, Lee Hsien Loong, to take over his post eventually. A retired brigadier general, the 37-year-old Lee Hsien Loong currently serves as trade and industry minister in his father's government.