Nyan Win, the party spokesman, said the National League for Democracy had expected to win around 60 percent of the vote but seemed on track to win more than 80 percent. He attributed the stunning margin to residual hatred of the military. But he also said the governing party was hurt by infighting, including the forced removal of its chairman just months before the election.

A study commissioned by the chairman earlier in the year warned that the ruling party might suffer steep losses, but the party leadership rejected the analysis, party members said.

“They have no unity,” Mr. Nyan Win said.

By noon on Saturday, the country’s election commission had announced the results for 478 of the 491 parliamentary seats contested in the election. The National League for Democracy has won 387 seats compared with the governing party’s 41. Smaller parties have taken the rest.

Complete results are expected Saturday afternoon, but Ms. Aung San Suu Kyi’s party has already won a majority, and with it the power to choose the next president.

For the past quarter-century, Myanmar’s military has been pursuing what the generals have called a road map to “discipline-flourishing democracy.” In 2008, they introduced a Constitution that they believed was sufficiently stacked in their favor. It reserves 25 percent of the seats in Parliament for the military, which meant that the military’s political wing needed only another 25 percent plus one to obtain a majority.

To seal the deal, the generals added a clause that bars Ms. Aung San Suu Kyi from the presidency. She has said she will choose the president and govern by proxy. She has also said she will seek to amend the Constitution, but the military has veto authority over amendments, setting up a political battle down the line.