PORT-AU-PRINCE, HAITI, DEC. 1 -- U.S. Embassy officials, guided by Washington's policy of support for Haiti's military government, were reluctant to conclude, despite a wealth of troubling information they received last week, that the armed forces would fail to protect voters in the elections Sunday.

Briefings with U.S. officials during the past two days have provided a picture of an adequately connected embassy gathering detailed local information but hampered from reacting by hopes that the Army could be trusted and by a surprising lack of leverage.

The elections collapsed Sunday amid a campaign of terrorist killing by allies of the fallen Duvalier dictatorship. The U.S. Embassy, headed by Ambassador Brunson McKinley, supported both the ruling National Government Council, headed by Gen. Henri Namphy, and the independent electoral council that he dissolved Sunday.

"I'm sure we had accurate information. Where we erred was in projecting it adequately," a U.S. official acknowledged today.

In a briefing only two days before Sunday's disrupted vote, an embassy political officer said there was "no indication" that either the government council or the Army would fail to respect the balloting and its results.

The officer also said Friday that the armed forces, of which Namphy this month named himself commander-in-chief, did not provide urgently requested helicopters to the electoral council because the council had not bothered to make a formal request. He based his assertion, he said, on what he was told by Army officers.

The electoral council frantically petitioned last week for the helicopters. The military's refusal to allow any helicopters to fly ballots and elections observers around Haiti was its first action in a concerted three-day effort over the weekend to subvert the election or, at least, stand by while terrorist gunmen disrupted it.

The political officer reportedly concluded privately only hours later that his interpretation was mistaken, but did not make his revised views known to reporters.

Also Friday, another of the embassy's three political counselors approached a New York Times reporter to dispute the veracity of his story reporting a roadblock set up on a main highway Thursday by armed Ton-Tons Macoutes, former members of a Duvalier militia. Thursday the Ton-Tons Macoutes were already threatening journalists and electoral officials at the roadblock, as Army and police troops looked on.

Other embassy officials reported that the armed forces commander in the north-central town of Gonaives near the roadblock was a well-known sponsor of local Ton-Tons Macoutes.

One political officer, when asked Sunday for help in rescuing American journalists trapped under Ton-Tons Macoutes' gunfire, advised going to the Haitian police, who had not appeared in the street during several hours of shooting.

But the embassy press officer, Jeffrey Lite, took his bulletproof van several times Sunday into areas where Ton-Tons Macoutes snipers were gunning for American journalists and pulled out the reporters.

"We received numerous assurances from the Haitian government the elections would come off," a U.S. official said today. "Our point of view was expressed many times that we held the government responsible for protecting the elections. Clearly they had other priorities that were more important than listening to a foreign power."

Canada and France also supported the electoral process.

U.S. officials said it had been a laborious task to rebuild U.S. influence with the government council after the 29-year isolationist Duvalier dynasty, ousted Feb. 7, 1986. Although Haiti suffers the most severe poverty in the hemisphere, the government council remained largely indifferent to a U.S. decision to nearly double U.S. economic aid to about $102 million in the past two years.

The Reagan administration frequently praised the sincerity of Namphy's commitment to democracy. The U.S. Congress, divided on the issue, provided only about $1.5 million in military aid to the 8,000-troop armed forces, for the purpose of peaceful crowd control training.

With commercial airline flights still irregular the U.S. Embassy today chartered a jet to fly out about 50 remaining American election observers.