The Committee in Solidarity with the People of El Salvador (CISPES) has been painted red by the White House. "Established with the assistance of the Communist Party U.S.A. and the Communist Party of El Salvador," Marlin Fitzwater, the president's press spokesman, said the other day, without a word to back it up.

"They have been saying it for years; we absolutely deny it," says Angela Sanbrano, executive director of CISPES, which the FBI investigated strenuously for about 3 1/2 years, using hundreds of G-men and a classified amount of money.

Sanbrano is remarkably calm for a woman who has so riled her government. She is 42 years old, with tranquil eyes and a serene brow. And when you talk to her for a while, you realize that she regards the whole matter as something of a tribute and even more of an opportunity.

"It is because of our success," she says. "We have a network here and in El Salvador -- they tell us what is going on down there and we spread the word. We are able to mobilize people in demonstrations against the Central American policy. Of course, I am angry at being smeared when I am doing something perfectly legal and trying to save lives. But I would rather talk about El Salvador. The killing has not stopped. It is getting worse."

As she stands in the neat, quiet CISPES offices on the second floor of a shabby building on 14th Street, an associate is standing by with a tape recorder, ready to play for a visitor the tape of a recent army raid on a refugee camp in San Salvador, complete with shrieks and sounds of gunfire.

CISPES is an organization with 55 chapters around the country and a loose, non-dues-paying membership of people from churches, student groups and human-rights organizations. Its hope is that the FBI's odious exertions will refocus the country's attention on El Salvador, which has sunk from sight while Washington fixes its gaze on Nicaragua and Sandinista compliance with the Arias peace plan.

No one remarks Salvadoran President Jose Napoleon Duarte's grotesque method of compliance with the plan's amnesty provisions. He has opened the jails and let out death-squad murderers who figured in the most notorious political killings of the early 1980s.

It is for this reason, some observers think, that, while the massacres of previous years have been sharply reduced, individual triggermen have grown bold again. This week brought a harrowing incident. The mutilated bodies of two men and a 14-year-old boy were found in San Jose, Guayabal. A dozen eyewitnesses swore that the three were grabbed on their way home from a party by members of the Army's First Brigade. The wife of one of the victims said her husband was murdered because he refused to become an army informer.

The auxiliary bishop of San Salvador, Gregorio Rosa Chavez, said at a televised Mass, "We are returning to the period when 40 bodies would appear every day along the highway . . . . "

The indifference to El Salvador suits the administration fine. The official line is that El Salvador is a struggling but model democracy ruled by a democratically elected leader whose decency is beyond question. The United States gives El Salvador $100 million a year in military aid. The war is in its eighth year, and the guerrillas control one-third of the country.

The reality, according to those who watch, is that Duarte is the prisoner of the military, powerless against its rabid elements and unable to institute the most modest reforms.

Americans who objected were subject to harassment and surveillance by the FBI, which infiltrated one CISPES office and sent agents to rallies and meetings to take down license numbers and photograph participants -- just as in the old days of Vietnam.

The FBI -- red-faced to be caught doing what its former director William H. Webster, now CIA director, swore it would never do again -- denies that it put out a dragnet for nonviolent opponents of President Reagan's policy.

If that is so, why did the quiet church of St. Patrick's in Cleveland become a target? Rep. Mary Rose Oakar (D-Ohio), who attends the parish, wants to know. So does her indignant pastor. The new FBI director, William Sessions, issued a preemptive whitewash of the investigation he is about to conduct: "I think what we will find will be quite proper."

Congress will do its own probe.

Angela Sanbrano is not worried about the outcome of either. All she wants is attention for El Salvador. She thinks people who take notice will come around to her view that the trouble there is not guerrillas but poverty, oppression and injustice. If the United States withdrew and a coalition government were formed, she believes, the country would stop being a graveyard for Salvadorans. Forty thousand have died since the civil war began.