YANGON, MYANMAR, MAY 28 -- The military government of Myanmar, formerly Burma, conceded today that the main opposition party was winning National Assembly elections with two-thirds of the vote and said it would hand over power after parliament agreed on a new constitution.

Foreign governments and opposition leaders had said before Sunday's elections that the army, which brutally crushed an uprising against the military government in September 1988, would try to delay handing over power.

Officials of the junta's information committee told a news conference that the military would play no role in drafting or approving the constitution. The officials did not say how long the process would take but Western diplomats said it could last as long as two years.

"If we had no intention of handing over power, we would not have had these elections," said Soe Nyunt of the ruling State Law and Order Restoration Council.

The multi-party elections Sunday were the first in Myanmar in 30 years, and diplomats said the voting was held fairly and freely despite months of intimidation and harassment of opposition candidates by government officials. The nation's leading opposition figures have been under arrest -- including two from the main opposition group, the National League for Democracy -- and were barred from contesting the election.

International human rights groups said before the elections that human rights violations were so widespread and restrictions on political expression so severe in Myanmar that a free and fair election was impossible.

The country's military leaders killed at least 1,000 people in the 1988 crackdown on a democracy movement that brought the hard-line government to the brink of collapse. Afterward, the government promised democratic reforms and legalized political parties for the first time since Gen. Ne Win took power in a 1962 coup.

The government has defended itself against critics who charged that the elections were being held to legitimize the military regime and enhance foreign investment. Authorities said that reforms were going forward slowly and noted that 2,392 candidates from more than 200 parties were allowed to contest the election.

The junta's information committee said today that the National League for Democracy had won two-thirds of the vote across the country so far. The league said that it had won 257 seats and lost eight, enough for a majority in parliament. A total of 485 seats were contested, with the vote in seven other precincts suspended for security reasons.

Pick-up trucks loaded with chanting league supporters and a crowd of onlookers around league headquarters were the only signs of overt celebration as results were announced. League candidates congratulating each other on their success said they were cautious about the days ahead.

"First we have to consolidate all our democratic forces and form a parliament and take power peacefully," said Naing Naing, member of parliament for the capital's Pazunduang district.

{In New York, the human rights monitoring group Asia Watch called on President Bush and other world leaders to urge Myanmar's government to respect the results of the elections and release all political prisoners. It also said Washington should use its influence with Myanmar's trading partners to refrain from new investments until a new government is allowed to take office and has guaranteed respect for fundamental human rights.}