YANGON, Myanmar — After struggling against the heavy hand of the Burmese military for two and a half decades, the opposition party of the Nobel Peace Prize laureate Daw Aung San Suu Kyi said Monday that it was confident of a sweeping victory in the country’s landmark nationwide elections.

Although official results of Sunday’s election trickled in for only a handful of districts, the potential electoral success by Ms. Aung San Suu Kyi’s political movement underlined the appeal of a woman who sacrificed her family, her health and 15 years of her life as a political prisoner to oppose dictatorship in Myanmar.

But it also portends a troubled and uncertain transition for Myanmar, and a dilemma for the military-backed government that until now has tried to manage the path away from isolation and dictatorship on its own terms. “Nationwide, we got over 70 percent,” said U Win Htein, a senior member of Ms. Aung San Suu Kyi’s party. He cautioned that the results were not yet official, but added, “We can call this a landslide victory.”

If the results of the election are respected by the current government and the military, it will be the first time in more than five decades that voters in Myanmar have been able to choose their leaders freely.