The lights were dimmed. The audience was told that no photographs or tape recordings are allowed and that the speaker from the National Security Council was attending at "great risk to his personal safety."

The senior NSC staff member, who recently returned from a three-week tour of Latin America, then began his pitch, part of a continuing White House effort to sell President Reagan's aggressively anti-communist policies in Central America.

After lighting a screen in the darkened room to display aerial maps showing Soviet military airstrips and bases, along with charts showing that Soviet military aid to Latin nations is now 10 times what the United States gives them, the career military officer pointed to a picture of concrete buildings on a desolate dirt road.

"I showed this picture to a man who had lived in a Siberian gulag for 25 years, and he said, 'Where did you get the picture of the gulag?' " the NSC staffer told the 75 persons gathered in the Old Executive Office Building next to the White House. "I told him this picture is not from the Soviet Union. It is from Nicaragua.

"He said, 'No, I lived in this gulag, I know the gulag.' I told him, 'My friend, time has passed you by. This is Nicaragua today.' "

Since the president went before a joint session of Congress to request increased aid to Central America, the White House's public liaison office has held weekly sessions with representatives of mostly conservative groups to sell the adminstration's policies.

"It's an uphill fight to get the American people to understand what we are facing down there is communism in our own back yard," said Faith Ryan Whittlesey, assistant to the president for public liaison.

"If you look at the polls, you'll see that people don't know what we are facing down there. We are starting from the very beginning, and we don't expect an instant success, but we are going to let people know what is at stake down there."

Whittlesey denied that the sessions are "preaching to the choir" of administration supporters. "Everyone is welcome," she said. "It's just that people who are already interested tend to show up . . . . But we have had requests from a labor group for a session and the Catholic Church has asked for a session."

The request from the Roman Catholic Church is considered particularly important because the administration has felt that church groups tend to portray leftists in Central America as romantic "Robin Hood" figures, in Whittlesey's words.

Last week's session for a group of Hispanic evangelists dwelled heavily on repression of religious freedom in Nicaragua. Before audiences with more substantial business interests, Whittlesey said, the economic importance of the region to the United States has been stressed.

For audiences more concerned with domestic issues, the stress has been on the impact of what the administration has portrayed as a flood of refugees from communism if more Central American countries come under communist control.

But for the Hispanic religious leaders, there was talk of how Pope John Paul II was mistreated and his homily drowned out by rebel chants when he traveled in Nicaragua. There was also the account of how a priest who served as aide to a Catholic bishop was lured to a woman's house and ordered to undress so a government agent posing as a cuckold could beat him before television cameras and have him arrested.

The speakers included two foreign officials, Salvadoran Ambassador Ernesto Rivas-Gallont and Paris Deputy Mayor Monique Garnier-Lancom (both of whom favor a strong U.S. stand against communism in Latin America), Otto J. Reich, the State Department's coordinator for public policy on Latin America, and Kerry Ptacke, Central America specialist for the conservative Institute on Religion and Democracy.

Every speaker condemned the U.S. media for not reporting the "Soviet, Cuban, Libyan connection" in Central America. Members of the audience also criticized the media. One man stood up to ask why American journalists do not report hundreds of people fleeing from Nicaragua to Honduras daily to escape communism.

Throughout the sessions, there are strong anti-communist images:

* Whittlesey saying the Soviet sickle or hammer can be found on some of the flags used by leftists trying to unseat the American-backed government in El Salvador.

* Reich arguing that doubts of the Soviets' intention to take over Latin America are similar to disbelief of Adolf Hitler's pledge to conquer Europe--"No one believed anyone could be quite that crazy. He was."

* Reich telling the Hispanics that the use of 55 military trainers in El Salvador is a U.S. effort to "conduct the war in a more humane manner and to gain popular support . . . . You do not address social problems with military means . . . , but also you don't address a military takeover . . . with a food-for-peace program or improved fertilizers."

Reich was particularly harsh with the media. He said that they had "not done a good job . . . . They are in business to sell advertising," and that American reporters have been gullible receptors for incorrect information that the U.S. government later "traced to the disinformation effort of the Nicaraguans."

Reich also suggested that the Reagan administration might consider running its own domestic information agency. But he added that, on second thought, the government "probably shouldn't."

The Hispanic evangelists also received a briefing packet containing Reagan's speech to the National Association of Evangelicals condemning the Soviet Union as an "evil empire," a picture of the president with an American flag rippling behind him, and a copy of an article he wrote condemning abortion.

The NSC staff member began and ended his talk in Spanish, and mentioned that he conducted a Wednesday night Bible class. He cautioned his audience against leftist appeals for the church in Latin America to promote revolution.

"I study the Good Book, and Jesus Christ never advised anyone to pick up a rifle," he said.

He described the administration's objective in Latin America as "protection of our the United States' security interests," and listed a four-point basis for administration policy in Latin America to which other speakers had referred as the four Ds: democracy, development, dialogue and defense.

He appealed to the Hispanics as Americans with jobs and an economy to protect by telling them that the 1980 Mariel boatlift of refugees from Cuba cost the United States $1.8 billion.

An influx from Latin America of 8 million refugees seeking jobs and homes, he said, would "cost the country in excess of $115 billion--but the cost goes beyond dollars to the democratic and racial problems it would cause and destruction of the economic recovery . . . . The human costs are incalculable."

The official then turned and pointed behind him to a picture of a lone child, shirtless and apparently lost on a barren dirt road. He identified the child as a Miskito Indian child "fleeing from internment camps in Nicaragua . . . . The child later died of malnutrition and parasites."