SAN SALVADOR -- Growing discontent in the Salvadoran armed forces and internal dissent in the ruling Christian Democratic Party are combining with El Salvador's perennial plagues of war and poverty to present President Jose Napoleon Duarte with one of his most difficult crises since he was elected three years ago, according to diplomats and government officials.

The combination of factors has raised the prospect of increased political violence and a return to the chaos of the early 1980s, the sources said.

The final results of the ongoing power struggle are unlikely to be known until after the next major changes in the leadership of El Salvador's powerful armed forces are announced at the end of the year, senior government officials and diplomats said.

"Duarte is like a one-armed juggler with seven things up in the air, and we will have to wait and see where they land," said one source who knows Duarte well.

The current unrest was fueled by two events last week: the return from exile of two leftist politicians allied with El Salvador's Marxist-led insurgents and the release by Duarte of new evidence linking rightist leader Roberto d'Aubuisson to the 1980 murder of Roman Catholic Archbishop Oscar Arnulfo Romero.

The two events aggravated the Duarte administration's relations with the military, already strained by the government's long-term efforts to build up a police force independent of the Army and by recent moves, such as the release of rebel prisoners and a unilateral cease-fire, to comply with a Central American peace plan.

Further exacerbating Duarte's troubles are the continuing toll of the eight-year-old guerrilla war, a declining economy, strong opposition from powerful business groups and eroding popular support.

Contributing to the atmosphere of uncertainty have been an upsurge in rhetoric and veiled threats by the country's extreme right wing following Duarte's accusations against d'Aubuisson. The charges, based on the testimony of a man who said he drove the getaway car, infuriated d'Aubuisson and goaded his Republican Nationalist Alliance (Arena) into its harshest attacks on Duarte in recent years.

The timing of the charges, the day before the left was to hold its first mass rally in seven years, allowed Duarte to play his favorite role as a political centrist. However, according to political analysts, the strength of that position has been severely undermined as his Christian Democratic Party engages in bitter and sometimes violent infighting amid a growing perception that the government is corrupt and incompetent.

The infighting has revolved around a battle in the party to succeed Duarte, who cannot run for reelection. Communications Minister Julio Rey Prendes appears to have gained the upper hand in the struggle over his closest rival, Planning Minister Fidel Chavez Mena, by dominating a recent convention to nominate candidates for legislative elections in March.

Many military officers resented what they saw as Duarte's attempts to make political capital of the charges against d'Aubuisson, a former major in the National Guard, knowledgeable sources said. These officers also found it difficult to stomach seeing leftist leaders Ruben Zamora and Guillermo Ungo, who returned after seven years of exile to begin political work inside the country, appear on television every day for a week, the sources said.

Zamora left El Salvador yesterday after a 12-day visit, and Ungo left on Sunday.

Officers were further stung when paid newspaper advertisements by groups on the far right charged that the military was shirking its duty by allowing the leftists to return.

"We consider the men to be terrorists; they are linked to the armed terrorists," said one top military official. "We do not think they should be here, giving press conferences and denouncing us. It is not right."

According to three sources who know the military well, there will be no orders for the Army or security forces to engage in the kind of officially sanctioned political violence that took thousands of lives in the early 1980s. But the sources said there now could be a higher tolerance for "free-lance" assassinations.

"There has been a loosening of the reins, especially among the mid-level officers," said one civilian who works with both the military and the government. "No one is giving orders that people be killed, but they are more willing to turn a blind eye now than a month ago, because they feel more threatened."

One top military officer said that he would follow orders not to harm the returning leftists.

"But I cannot speak for the soldiers who watch them and may want revenge if the terrorists killed someone in their family," he said. "I think that, yes, political violence can increase sharply."

Christian Democratic leaders said they fear Duarte may have begun a process he cannot control by blurting out the charges against d'Aubuisson and giving a heavy political cast to the case. Sources close to the investigation said two more witnesses were being tracked down in the United States and that the government planned to present other evidence to corroborate the initial charges. They said they had wanted to wait until everything was in place.

"He just could not wait, but that is Duarte," said one close adviser. "Unfortunately, he may have permanently tainted the case, which we think is very solid."

In a move seen as aggravating Duarte's already rocky relationship with the military, d'Aubuisson's counterattack has centered on one of Duarte's few staunch allies in the Army, Col. Reynaldo Lopez Nuila, currently vice minister for public security.

"Arena and the right are appealing to every point of disquiet in the armed forces, trying to widen the split between Duarte and the Army and the desk commanders and field commanders," said one diplomat.

D'Aubuisson charged that Romero's killing was the work of the National Police, which Lopez Nuila commanded at the time of the murder.

Lopez Nuila, who has never had a field command, is disliked by senior military commanders, at least in part because he is pushing to create a police force that receives separate training from the regular Army, and has overseen the establishment of a police academy.

Many in the military believe he is trying to create a separate force that would be equal to the Army when the military's strength shrinks after the war, insiders said.

"That man over there," said one top officer, gesturing toward Lopez Nuila's office, "is trying to duplicate our structures, duplicating intelligence operations, duplicating chains of command, dividing the military. It is counterproductive to us."

Both the returning leftists and Arena have used increasingly harsh anti-American rhetoric in attacking the government. Duarte is one of the staunchest U.S. allies in Central America, receiving $1.5 million a day in American economic and military aid.

"All Duarte has left solidly supporting him now is the United States," said one of the president's advisers. "I hope that is enough."