letter from El Salvador has been delivered to each member of the House and Senate. Its intensity assures that only those calloused to pain can ignore it. The writer is Arturo Rivera y Damas, the Catholic archbishop of San Salvador.

The letter is stirring. It is also jolting. Rivera y Damas isn't another Third World beggar asking for an American crumb. With bluntness, he tells members of Congress that "the authorities and members of the government of the United States have closed their doors and their hearts against the suffering of my people." In six paragraphs, the successor to the martyred Archbishop Oscar Romero appeals to Congress to ease "the agony of my flock in search of refuge."

The doors he talks about are the iron ones of the Immigration and Naturalization Service (INS). With unique rabidity, the agency blocks Salvadoran refugees from entering the United States and then deports as many as possible of those who do slip in. An estimated 100 Salvadorans are returned each week.

Where is your mercy, asks the archbishop: The war in El Salvador "continues to grow" and as a result "there are almost a million Salvadorans who are displaced or have become refugees." The United States, which is the only Central or North American country that systematically ships back Salvadorans, has an estimated 300,000 undocumented aliens from El Salvador. Most of that number turned up after 1980, when the skirmishes became a war and Congress and the Reagan administration became willing partners in it.

The jolt in the Rivera y Damas letter is found in more than the accusing finger that he points. He involves himself in U.S. politics, as American politicians have involved themselves in El Salvador. Rivera y Damas asks Congress to pass legislation that would extend voluntary departure status to illegal aliens. The bill he specifically mentions has been introduced by Rep. Joe Moakley (D-Mass.) and Sen. Dennis DeConcini (D-Ariz.). One of its purposes is to put a two-year hold on deportations. By then, presumably, the country will be safe enough for returns. If not, Congress could extend the status.

Extended voluntary departure has been a protection offered in recent years to illegal aliens from Poland, Afghanistan and Ethiopia. Moakley, who has been joined by 171 cosponsors in the House, argues the obvious, that a double standard is at work: "The facts, documented by every major human-rights organization in the world, show that the general conditions of violence in El Salvador are at least as bad -- if not worse -- than what is happening in Poland today. Why do we help the Poles but not the Salvadorans?"

An answer to that -- if answer is the word -- was supplied last April when Elliott Abrams of the State Department testified before the Senate. Wise up, Abrams counseled: The deportees are not meeting persecution and death in El Salvador; that's only the scare talk of some "activist" human-rights groups.

Abrams went on to portray the Salvadorans as greedy opportunists who have come to America to sniff out the Yankee dollar. The search, apparently, has been fruitful. Somehow Abrams came up with a figure of "$30 million" that is sent each month by Salvadorans in the United States to their relatives at home. That's $360 million a year, which is 72 percent of the entire 1983 revenues for the government of El Salvador. Illegal aliens are either winning a lot of lotteries or the wages of dishwashers, maids and busboys are booming in ways that nobody but Abrams knows about.

Upwards of 50,000 people have been killed in the Salvadoran war. That number still does not seem high enough for some. A year ago, Sen. Alan Simpson (R-Wyo.) said that it was only the cranks who had it wrong: "Some strident and often partisan critics of current policy would have us believe that the violence in El Salvador prevents anyone from living there with any reasonable expectation of personal safety. This is most assuredly untrue."

This reflects the create-a-desert- and-call-it-peace school of thought. With 50,000 people dead in a country of 5 million -- and large numbers of those deaths at the hands of government agents -- some calm is bound to return. Fewer people remain alive.

Aside from observers like Abrams and Simpson (one sees El Salvador becoming green with American billions, the other as a land of safety), most others agree with the version of Rivera y Damas, that El Salvador is an impoverished nation being leveled by war and persecution. An estimated 50,000 Americans in some 200 churches and synagogues are giving sanctuary to illegal aliens. The city council of Los Angeles calls for public officials to ignore the illegal status of Salvadorans. Similar actions have been taken in Chicago, New York and St. Paul, Minn.

What is Congress waiting for? In case the message of civil disobedience from American cities and churches isn't clear enough, Rivera y Damas says it all in one line: "To return the persecuted to the source, the origin and the cause of their suffering is an act of injustice in the eyes of Christian love."

The archbishop says to Congress: Open your arms. Congress has been answering: No, we'll send you arms.