According to President Reagan, "a determined propaganda campaign has sought to mislead many in Europe and certainly many in the U.S. as to the true nature of the conflict in El Salvador.

"Very simply," Reagan said in his Feb. 24 speech to the Organization of American States, "guerrillas armed and supported by and through Cuba are attempting to impose a Marxist-Leninist dictatorship on the people of El Salvador as part of a larger imperialistic plan."

As the administration seeks support for stepped-up U.S. involvement in Central America, it has become embroiled in an increasingly emotional debate in this country between those who support its policy and those who question not only U.S. actions, but the premises on which they are based.

To counter Reagan's description of the Cuban-based genesis of El Salvador's civil war, others, including members of the U.S. Roman Catholic hierarchy and some members of Congress, offer a version maintaining that the war is an indigenous uprising that, while perhaps aided and promoted by Cuba, springs from local rage against historic economic inequities and military repression.

Opponents of U.S. policy charge that the administration ignores available facts that would undermine its case and exaggerates what it feels is supportive to a misbegotten and ultimately counterproductive policy.

Many in the administration say that underlying the opposition is a worldwide "disinformation" campaign, orchestrated by the Soviet Union through activists in this country who feed false information to the unsuspecting--including in some cases the U.S. media.

In what has become a virtual cottage industry of Central America-related information, a steadily growing number of nongovernmental organizations on all sides of the issue strives to influence U.S. public opinion and policy-makers in Washington.

Complicating the difficulty of taking a dispassionate view of events in Central America are wild rumors and exaggerations coming out of the region. Because many atrocities--including mass murders, mutilations, torture and kidnapings--have been documented, there is a tendency to believe and disseminate similar stories that later turn out to be false, or unverifiable.

Last year, for example, a human rights group in Honduras reported that more than 1,000 people who had taken refuge in a cave in El Salvador were killed when government forces bombed or otherwise sealed shut the entrance of the cave. The story was picked up and spread by the guerrillas' clandestine radio and the Cuban and Soviet news media.

Heather Foote, of the church-funded Washington Office on Latin America, follows developments in El Salvador in minute detail and opposes U.S. policy. She said many rights groups and independent journalists investigated the report, but none was able to confirm it. Although her organization and others in the United States decided not to publicize the report, it was picked up by some news agencies.

Incidents like this, Foote said, are "unfortunate," because they "enable people to discredit reports of real massacres." Supporters of the Salvadoran government headed by Jose Napoleon Duarte point to exaggerated reports of abuses as evidence that all such reports are inaccurate.

In a recent speech, Secretary of State Alexander M. Haig Jr. attacked the leftist government of Nicaragua, which the United States charges is aiding the Salvadoran rebels. As proof of what he called Nicaragua's "atrocious genocidal actions" against the anti-Sandinista Miskito Indians of Nicaragua he referred to a photograph published by Figaro magazine in Paris of burning bodies identified as Miskitos.

The magazine later acknowledged that the photograph actually was taken in 1978 during the Sandinista-led insurrection against dictator Anastasio Somoza and depicted Red Cross workers burning the bodies of casualties for hygienic reasons.

Each side interprets the information available from the region in the light of its own perspective.

Organizations fueling the "information war" over Central America include activists both opposing and favoring U.S. action against leftist insurgencies; church groups with missionaries in the area; business organizations, labor unions and conservative and liberal think tanks and public-policy groups.

All seem to gather their information from similar sources--U.S. and foreign publications, radio broadcasts, government reports, congressional hearings and visitors from Central America.

Aside from then putting out different versions of what is happening in Central America, the groups speak to different audiences with varying degrees of effectiveness. The "solidarity groups" that support the revolutionary government of Nicaragua and the leftist insurgents in El Salvador and Guatemala appear to influence mainly those already sympathetic to their cause.

The many church and labor union groups that have taken an interest in Central America seem to have more influence on Capitol Hill and back home among their constituents than in the executive branch of government. After many years in the cold, the conservative publications and think tanks have the ear of this government's policy-makers. A number of former members are now in the government. These groups' research and conclusions are reflected in government statements.

Business groups have the resources and political clout to make their views heard in both Republican and Democratic administrations.

Sources inside and outside the government agree that Catholic and Protestant churches have become a major influence in the debate. Since many U.S. denominations have had missionaries in the region for years, local congregations and the national headquarters of the churches have received firsthand reports of conditions there.

Both the Catholic Church and major Protestant denominations have issued statements opposing military aid to El Salvador and Guatemala and critical of the anticommunist orientation of the Reagan administration's policy.

Rep. Michael D. Barnes (D-Md.), chairman of the House subcommittee on inter-American affairs, said: "The group that has the most credibility and that I sense is listened to most by my constituents is the Catholic Church. I'm not sure how they mobilize people, but they are certainly well-mobilized."

Among the church groups working to mobilize people against administration policy are the Religious Task Force, made up of Catholic religious orders, and the Inter-Religious Task Force, an ecumenical coalition of Protestant, Catholic and Jewish groups. Both groups gather information on Central America that they send to churches around the country to be used in letter-writing campaigns, meetings with congressmen and demonstrations.

A church-oriented group of growing importance in opposing administration policy is the Washington Office on Latin America. Founded in 1974 by a retired businessman and a Methodist missionary on furlough with a budget of $4,000, it has expanded to an active organization with a staff of eight or nine and a budget of $250,000.

"The real initiative came from organizations with missionaries in Latin America who were getting information from their personnel that it seemed as if U.S. policy was undermining their ability to conduct their mission," said Joe Eldridge, the former Methodist missionary who is now director of the office. "The churches came to the conclusion that they didn't have the foggiest idea how policy was made and since they had a substantial investment in Latin America it was logical that they would want to keep themselves apprised of the evolution of U.S. policy."

WOLA puts out reports to the churches, press releases and a newsletter. It provides people to testify at congressional hearings and helps set up appointments and interviews for visiting representatives of such Latin American opposition groups as the Democratic Revolutionary Front, the political coalition allied with the insurgents in El Salvador.

Eldridge said most of the office's funding comes from 40 churches and a few foundations. The only foreign source of funds, he said, is the World Council of Churches.

Another church-oriented group, the Institute for Freedom and Democracy, has a different perspective. Last August it sent a packet of material defending the Duarte government in El Salvador to about 2,000 clergy and lay people.

Penn Kimble, a writer who now works as a consultant for the institute, said it was founded early in 1980 "by a group of people who felt that the debate in the religious community . . . didn't properly address some of the questions about democratic values that we thought were important."

He added: "We felt there was a polarization of opinion in the religious community between the reactive right and the unthinking and careless left, where the views of many American churchgoers just didn't have a voice."

The organization provides training programs, speakers and informational materials for local and regional church groups. It has put out publications critical of the Sandinista government in Nicaragua and the leftist opposition in El Salvador, including an introductory brochure criticizing national Protestant and Catholic headquarters for supporting leftist causes abroad.

While church groups are relatively new in influencing foreign policy, there are several business-oriented groups that have influenced Latin American policy for years.

Recently, at the urging of David Rockefeller, retired chairman of Chase Manhattan Bank, three of these organization formed a new umbrella group called the Americas Society. Sam Hayden, president of the Council of the Americas, said his organization and the Center for Inter-American Relations and the Pan American Society hoped to coordinate their fund-raising and what he described as educational activities. A fourth group, the State Department-backed Caribbean-Central America Action, is considering membership.

Hayden said the Council of the Americas, made up of 200 corporations with investments in Latin America, provides information from Washington and Latin America to its members as well as seeking to influence U.S. policies on certain issues. It supported, for example, the Panama Canal treaty and aid to the new government of Nicaragua.

Hayden said the council has taken no position in the debate over whether the United States should increase its military role in Central America, because its members disagree on the issue.

The council and Caribbean-Central America Action, headed by former State Department official Peter Johnson, submitted ideas to the government for President Reagan's recent speech to the OAS proposing the dropping of tariff barriers and increased economic aid for the Caribbean and Central America.

Johnson said that from the perspective of the "moderate businessmen" his organization works with in Central America, "the moderate center of political leadership," including Salvadoran President Duarte, "deserves solid support."

The AFL-CIO's international office and its American Institute for Free Labor Development generally support the government of El Salvador, and have testified to that effect in congressional hearings. The institute has a contract from the Agency for International Development to give technical assistance to El Salvador's agrarian reform.

Other unions, including the United Auto Workers, support organizations that oppose administration policy, such as the Council on Hemispheric Affairs and the Labor Committee for Human Rights and Democracy in El Salvador.

Three "solidarity" groups--Committee in Solidarity With the People of El Salvador (CISPES), Network in Solidarity With the People of Guatemala and the National Network in Solidarity With the Nicaraguan People--particularly raise the ire of their counterparts who back Reagan.

The three groups have similar histories and work closely together out of a crowded office decorated with revolutionary posters in the Dupont Circle area. Together with other activist groups, they are sponsoring demonstrations against U.S. military involvement in El Salvador in Washington and three other cities March 27, the day before the Salvadoran election.

The solidarity groups are "networks" of local organizations opposed to U.S. action against Nicaragua and the insurgents in El Salvador and Guatemala. Some members were involved in the movement against the war in Vietnam, others lived in Central America as Peace Corps volunteers or missionaries.

All three groups say they are supported by large and small individual contributions and some foundation grants. They deny reports that they receive money from leftist governments or organizations abroad. A report by Bruce McColm of Freedom House in New York City charges that CISPES, which one U.S. official described as part of the "big lie" network on Central America, was organized by Farid Handal, brother of the head of the Salvadoran Communist Party, and has received money from the U.S. Peace Council, affiliated to the Soviet-backed World Peace Council.

McColm and other writers have attributed the report about Handal forming CISPES to a captured guerrilla document made available by the State Department last year. The document, purportedly Handal's report on a trip to the United States in February of 1980, describes meetings with several people involved in activities opposing U.S. military aid to El Salvador and his efforts to encourage them to work more closely together.

Rob Costa of CISPES said that although the U.S. Peace Council is a member of the organization's advisory board, it contributes no money. He and other CISPES staff members denied that Handal had anything to do with organizing it.

Because of the growing U.S. involvement in El Salvador, CISPES is the most active of the three groups, with more than 300 local committees around the country, many on college campuses. These groups sponsor demonstrations and teach-ins, distribute publications supporting the Salvadoran opposition, raise money for Salvadoran refugees (distributed through the archbishop of Cuernavaca, Mexico) and work with others to lobby members of Congress.

Former U.S. ambassador to El Salvador Robert E. White, now at Carnegie Endowment for International Peace, describes CISPES as "immensely powerful." "On every college campus in the country, when I go to speak I get questions so detailed . . . . There are kids out there in those universities that follow this thing with single-minded devotion."

White also said CISPES is "one-sided" in the way it chooses and presents information.

Members of CISPES said the organization gets its information about the conflict in El Salvador from SALPRESS, a news agency with ties to the guerrillas; from U.S. and Latin American media, and from people who have recently visited Central America.

Opposing CISPES on many college campuses is the Collegiate Association for the Research of Principles, or CARP, the youth organization of the Rev. Sun Myung Moon's Unification Church. Dan Fefferman, headquarters director of CARP, said it distributed 1.5 million leaflets supporting the Duarte government and Reagan's policy in El Salvador last year. The group, which sponsors residential houses on college campuses, also holds "counterdemonstrations" during protests against administration policies.

Which of these groups influences administration policy? "I don't know," said Rep. Barnes of the inter-American affairs subcommittee, and other Central American specialists echoed his perplexity.

Most often mentioned by outside observers as influences on administration thinking were conservative-oriented think tanks such as the American Enterprise Institute, the Hudson Institute, the Heritage Foundation, the Center for Strategic and International Studies at Georgetown University and the Council for Inter-American Security.

The Heritage Foundation, which issued a report critical of the Sandinista government in Nicaragua last week, sends its publications to "every congressional office, people in the executive branch and several thousand people in the media," according to Jeff Gayner, director of foreign policy studies. The foundation, which also has a "talent bank" to find jobs for conservative professionals, has a $5 million budget based on contributions from corporations, foundations and donations averaging $25 from about 125,000 individual contributors, its 1980 annual report said.

Publications of the Council for Inter-American Security emphasize Soviet activity in the Western Hemisphere. The council campaigned against the Panama Canal and SALT II treaties and has published booklets on Central America.

Gordon Sumner Jr., a retired general and chairman of the council, was named special adviser to Secretary of State Haig, and Roger Fontaine, a director, is senior staff member for Latin America on the National Security Council.