Japanese and French archeologists have helped Vietnam prepare the bid for the Thang Long Imperial Citadel site for recognition by UNESCO, said the Vietnam News Agency.
Vietnam hopes to have the citadel listed before Hanoi celebrates its 1,000th birthday in 2010, and workers are now excavating palace structures and artifacts at the site, which is closed to the general public.
Hanoi became the capital of Vietnam in 1010 under the Ly Dynasty, and was then known as Thang Long, or Ascending Dragon, symbolizing the desire for independence after a millennium of Chinese domination.
The remains of the ancient citadel and relics from five feudal dynasties were first discovered in 2002 during excavation work to build a new national assembly in the center of the capital, putting construction on hold.
Archeologists found thousands of artifacts, including terracotta figures of dragons and phoenix heads, ceramics, cannons, swords and coins.
The dig unearthed ancient palace foundations and the remains of the central forbidden city, with ruins dating back 1,300 years to the Chinese Tang dynasty.
The find started a dispute between heritage and development forces over what to do with the ruins located in what has been Vietnam's center of political power for much of its history, from ancient times until today.
The 20,000-square-meter (200,000 square-feet) dig shared a city block with the former Ba Dinh national assembly and is located near the mausoleum of Ho Chi Minh, Vietnam's revolutionary leader and first president.
The assembly was demolished this year and a new one will be built on the same site, allowing the adjacent ruins to be saved, officials have said.
The ancient ruins were designated a national architectural and historical relic site in February, when Deputy Minister of Culture, Sports and Tourism Tran Chien Thang pledged to preserve the vestiges of the citadel.