SAN SALVADOR, DEC. 27 -- The Christian Democratic Party of President Jose Napoleon Duarte is so divided over choosing his successor that it is likely to lose its fragile majority in the National Assembly in elections early next year, according to senior party officials, diplomats and analysts.

The loss would jeopardize the political and economic changes that Duarte initiated and staked his reputation on carrying out. A split between the party's two most powerful leaders could also open the door for the far right to win the 1989 presidential elections, something many analysts say could trigger another round of indiscriminate bloodshed.

The United States, which pumps $1.5 million a day in economic and military aid into El Salvador and is Duarte's biggest supporter, could also stand to lose if the militant far right wins and seeks to roll back policies enacted by the Christian Democrats, the same sources said.

Rightist leaders Roberto d'Aubuisson of the Arena party and Sigifredo Ochoa, a recently retired colonel, have blamed the United States for the military's failure to defeat the leftist insurgency and for the nation's economic crisis, which they say is the result of U.S.-backed reforms.

Elections for the 60-seat unicameral Legislative Assembly and municipal officers are scheduled for March 28 and are widely viewed as a preview to a bitter presidential election in 1989.

Much of the conflict over nominations of candidates for the assembly has reflected a more personal contest between two candidates for the Christian Democratic nomination to succeed Duarte: Julio Rey Prendes, a party pro who has control of its machinery but is accused by his opponents of being corrupt and unreliable, and Fidel Chavez Mena, a younger, more conservative technocrat.

Many in the party accuse Duarte of allowing the infighting to grow so bitter and say the weakening of the party is largely responsible for the leader's waning popularity and the flow of power back to the military.

By law, Duarte cannot run again, and he has promised to remain neutral in the fight to succeed him. But many party officials say he should take a greater role in reining in the contenders.

"Duarte's behavior has been bad, bordering on irresponsible," said a founder of the party. "He cannot just wash his hands of the party like Pontius Pilate."

Last month, Duarte, in a speech at a party convention acknowledged problems and urged the party remain united, but otherwise he has remained above the fray.

The auxiliary bishop of San Salvador, the Rev. Gregorio Rosa Chavez, in a brief interview today, said avoiding violence in the elections was politicians' biggest challenge.

"We have a great fear, and I think it is generalized, that the politicians will not find a way to conduct a campaign without generating violence," he said after his homily at the Metropolitan Cathedral. "The work of the politicians has not been up to the level required by our national problems, and we hope they bear in mind the people's desire to avoid violence in 1988."

"The split is the root of many of the our problems, including with the military," said a party elder. "Duarte used to be able to call on the rank and file of the Christian Democrats as a counterbalance to the {officer corps}, but now, as we have lost the confidence of the people and are occupied with our own fighting, it is felt in every other area."

Recent polls show a growing number of respondents believe no party is capable of solving the nation's civil war, the close to 50 percent unemployment and a declining standard of living.

According to an October poll of 941 adults conducted by the University Institute of Public Opinion of the Jesuit-run University of Central America, only 6 percent supported the Christian Democrats, while 10 percent supported the far-right Republican Nationalist Alliance, or Arena.

It was the first independent poll to show Arena, led by d'Aubuisson, leading the Christian Democrats. But more surprising was the 76 percent who felt no party represented their interests. (The poll preceded Duarte's recent charge, based on new evidence, that d'Aubuisson instigated the killing of Archbishop Oscar Romero in 1980.)

"This is more dangerous to the democratic process here than the rebels," said a leading Christian Democrat. "All the political parties have lost the faith of the people, and that can do more damage than the guerrillas."

In the contest between Ray Prendes and Chavez Mena, the U.S. Embassy is officially neutral. But diplomats say Chavez Mena is strongly favored by the United States, and by Western Europeans and sectors of the military.

Both men recently resigned Cabinet posts to pursue the nomination. Followers of Rey Prendes, 55, won 12 of the 14 provincial elections naming candidates to run for the assembly in March, failing to renominate any of the 13 standing deputies who favored Chavez Mena.

Followers of Chavez Mena, 48, say the followers of Rey Prendes threatened, bribed and cheated to win those elections. No independent evidence has been presented to prove the charges, nor other general charges of corruption.

"We lost because our leader used democratic rules, and they used the law of the jungle," said a leader of the Chavez Mena forces. "It is that simple."

A spokesman for Rey Prendes said the charges were false, and were made because the losers were less well organized and could not accept the democratic outcome of the provincial caucuses.

Christian Democrats now hold 33 seats in the assembly, while Arena holds 13, the National Conciliation Party 12 and smaller parties the remaining two. The last election was in 1985.

Duarte's brand of Christian democracy is considerably to the left of affiliated Christian Democratic parties in Western Europe. The party's three-seat majority has won him approval of his legislative programs, including economic changes, accelerated land redistribution, an amnesty and a revised electoral law without having to make deals with the right.

Two weeks ago, 13 supporters of Chavez Mena in the assembly threatened a public break with the party because of what they charged was misconduct by Rey Prendes' forces. Last-minute negotiations averted the action, party sources said.

But party leaders estimate the Christian Democrats could end up with only 24 to 26 seats in March, forcing them to cut deals or face a halt in their projects, most of which are opposed by the right.

Several analysts said they expected Arena, the best-funded and most articulate opposition, to end up with close to 20 seats.

A new leftist alliance called the Democratic Convergence, made up largely of political allies of leftist rebels who recently returned from seven years of exile, is considering contesting as well.

Juan Jose Martel, a member of the group's directorate, said one factor was whether the alliance could pick up enough disgruntled Christian Democrats to win several seats and perhaps hold the balance of power. Martel and many of the other members of the leftist groups were Christian Democrats before splitting off in 1980 and going into exile.

"I never thought it would be possible the Christian Democrats would do to each other what they are doing," Martel said. "They are not even a shadow of what they used to be."

The electoral process was begun as an alternative to Nicaragua's leftist revolution and is largely aimed at defeating El Salvador's Marxist-led insurgency through a "democratic revolution." Since 1980, the United States has pumped close to $3 billion in economic and military aid into the Massachusetts-sized country, making it one of the most dependent in the world.

Chavez Mena ran against Duarte for the Christian Demcratic nomination in 1984, then turned down Duarte's invitation to run as vice president. Those who know him say he is intelligent but comes across as cold. He has not worked in organizing the grassroots party, as has Rey Prendes.

However, according to diplomatic sources, the United States and Western European community, which provide El Salvador's economic lifeline, view Chavez Mena as a more viable and reliable candidate. He recently resigned as minister of planning, where he administered most of the U.S. economic aid.

Rey Prendes has been a long-time Duarte ally and has worked with the party rank and file. He has a reputation for being able to cut a deal with anyone, an attribute, observers say, that makes the military fear he could negotiate something with the insurgents.

While Chavez Mena is going to dedicate himself to his presidential campaign, Rey Prendes is running for the legislature with the objective of launching his presidential candidacy from there.

Party members' big fear is that after one loses the nomination, he will not work for the other.

"It was different with Duarte, because everyone got behind him," said a veteran. "This time, I do not think Rey Prendes' people will work for Chavez Mena or vice versa. It could be the end of us."