The patriotic march for Central America's Independence Day here last Sunday was similar to those of past years. What was different was the "countermarch" by leftist union members to complain that President Jose Napoleon Duarte has failed to keep his promises to them.

To an extent unthinkable even a year ago, leftist groups are visible now in El Salvador, declaring in the streets what they once dared to say only in whispers for fear of death squad retaliation.

At the same time, the far right is splintered and relatively quiet. Its unquestioned leader, Roberto d'Aubuisson, head of the right-wing Nationalist Republican Alliance, or Arena, which lost to Duarte in last spring's elections, surfaced earlier this month to complain about an advertisement criticizing him, and the joke was, "Roberto who?"

D'Aubuisson's former second-in-command, Hugo Barrera, has split to form a new party, Patria Libre, or Free Country, which he says will be "much more moderate" than Arena.

The overall result seems to be rising political noise but lowered political tension of the sort that has meant riots, massacres or military coups here in the past.

Signs that some democratic trends are spreading, however, are mixed with other realities. The 5 1/2-year-old guerrilla war continues with no sign of renewed dialogue between the insurgents and the government. The noise reflects real discontent and a foundering economy that may yet sink Duarte. And political violence took at least 218 civilian lives before Aug. 1 this year, according to the U.S. Embassy's conservative count. Other tallies are higher.

However, the death squads no longer make public threats or publicly claim responsibility for recent killings. None of the estimates of the number of persons killed this year equals the total number of killings in a two-week period in 1981.

Many more people are speaking out openly.

Recently there have been peaceful marches and demonstrations demanding higher pay for doctors, social security office employes, peasant cooperative members, teachers and hospital workers. There have been strikes by pilots of the national airline, the hospitals, waterworks employes and bus drivers, and even a work stoppage at the Treasury Ministry.

Three groups of mothers marched last week to protest the Honduran government's treatment of Salvadoran refugees and Radio Venceremos, the clandestine guerrilla radio, called on workers for weeks to join last Sunday's union rally. At the reopened National University, students again are denouncing Duarte in regular meetings. But several recently fled the country after reporting threats against their lives.

The security forces keep a close eye on all these events, but so far there have been few arrests. In an interview, the defense minister, Gen. Carlos Eugenio Vides Casanova, said the armed forces had "ignored four or five critical situations recently in which at one time we would have considered a coup in order to save the country."

He listed the initiation of dialogue with the guerrillas last year, the turbulent election campaigns of 1984 and 1985 and the recent guerrilla kidnapings of 14 mayors. He was interviewed before the Sept. 10 kidnaping of Ines Guadalupe Duarte Duran, the president's daughter. The Associated Press quoted officials as saying Friday that seven more mayors had been kidnaped since Thursday.

"We now understand that in the weakness of a democracy, that is, in its divisions, is also its strength," he said. "We demonstrate our maturity by not intervening."

Few here believe, however, that the armed forces would tolerate widespread disorder or a long general strike. The estimated 80,000 organized or affiliated workers are deeply divided along political lines and still keep their marches short.

Julio Cesar Portillo, 39, head of the National Association of Teachers here, said teachers believed Duarte when he blamed their low pay and the stalled agrarian reform program on the Nationalist Republican Alliance.

"He said 'Vote for us and it'll change,' so we did, but nothing has happened," Portillo said. "Duarte has lost his moral force . . . . It isn't that he can't negotiate with us; it is that he doesn't want to."

In an interview, Duarte said the teachers used to turn out 20,000 demonstrators against the military government. The protesters "are in their weakest moment" now, and most of them "are managed by the rebel coalition FMLN," including the teachers, he said. "The people know we're working under difficult conditions, and I have said clearly there will be no miracles."

On the right, there is some anger that the government openly allowed journalists to enter a militarily restricted zone recently to interview guerrilla commander Joaquin Villalobos. One prominent businessman said he was "offended" by the title of a leftist peasant union's new weekly radio talk show, "Proletarian Dawn."

A Duarte adviser said there had been a decision that such things hurt the guerrilla cause more than they help it by "exposing how empty the rhetoric really is."

Barrera said his new party, which is widely regarded here as backed strongly by the U.S. Embassy, differs from Arena because a council will make its decisions, not just one man.

Agrarian reform must be consolidated and completed, Barrera said, not rolled back; guerrillas seeking amnesty should not only get it and 1,000 colones (about $200) for their weapons as they do now, but also a job and a place to live, he said.

In Arena, Barrera said, "We did things two or three years ago that had justification then. But things have changed, and we have to be much more moderate now."