The nation's two largest conservative parties tonight called for annulment of Sunday's nationwide legislative and municipal elections in which their moderate Christian Democratic rivals claimed a sweeping victory, the nation's top elections official said.

Mario Samayoa, president of the Central Elections Council, said in a televised broadcast that the right-wing Nationalist Republican Alliance and the conservative National Conciliation Party had charged irregularities in the elections.

Roberto D'Aubuisson, leader of the Nationalist Republican Alliance, was quoted by The Associated Press as saying: "Ballot boxes disappeared, were transported from one place to another without official observation, and were stuffed."

The challenge apparently surprised Christian Democratic leaders including President Jose Napoleon Duarte and upset what had seemed to be a calm atmosphere here. It was unclear whether the conservatives were seriously seeking to overturn the elections or were just trying to save face with their supporters, political observers said.

In a surprising twist, the two conservative parties alleged in their petition to the elections council -- on which they hold a two-to-one majority -- that the Armed Forces had aided the Christian Democrats in the election, Samayoa said.

"They are involving the Armed Forces, which they accuse of having participated in favor of a certain political institution," the elections council president said.

D'Aubuisson is a former Army major, and the military establishment is considered conservative. But the Armed Forces have insisted that they acted in the election only to safeguard the democratic process, and the Christian Democrats praised what they called the military's neutrality in the election.

It was not clear what role the conservative parties charged the Armed Forces to have played. But sources cited several rumors that military personnel had accompanied government officials who confronted poll watchers of the conservative parties, and had searched homes of conservative supporters.