In his weekend pleas for military aid to rebels in Nicaragua, President Reagan drew on the bywords of 40 years of staunch anticommunism to paint a dark and ominous picture of the Marxist government of Nicaragua and the threat it poses to the United States.

To make his grim portrait, the president invoked some disputed statistics and accusations and a panoply of devil figures, from Italy's Red Brigades to Iran's Ayatollah Khomeini. In the end, Reagan suggested that Congress' upcoming votes on the $100 million aid request will determine the course of the entire East-West conflict.

Grimmer versions of the appeal were drafted, according to White House officials. Those drafts included two grisly examples of alleged atrocities by the Sandinista rulers of Nicaragua in addition to the two Reagan used, the officials said.

On Saturday, Reagan charged in his regular nationwide radio address that Nicaraguan operatives "dress in freedom fighter [rebel] uniforms, go into the countryside, then murder and mutilate ordinary Nicaraguans." Asked for evidence, a senior official briefing reporters said it came from "sensitive intelligence sources that I'm not going to get into."

One of those is presumably a Sandinista defector, Alvaro Baldizon, who made the charge at a news conference two weeks ago but provided no evidence.

On many other points in his radio talk and in a nationally televised speech Sunday, Reagan used disputed information to draw a stark, black-and-white image of the Nicaraguan situation. For example:

*His portrait of the counterrevolutionaries, or contras: "When the Sandinistas betrayed the revolution, many who had fought the old Somoza dictatorship literally took to the hills . . . . [Today they have] more than 20,000 volunteers, and more come every day."

A 1982 Defense Intelligence Agency summary described the early contra groups as mainly remnants of Anastasio Somoza's National Guard, one of which, the "15 of September Legion," had carried out "terrorist" acts, the DIA said.

Provided with Central Intelligence Agency funding and advice beginning in 1982, the contras began to grow, recruiting an army of peasants unhappy with the Sandinistas. Their political leaders, held together in uneasy unity by CIA prodding, are civilian critics of the Sandinistas or disaffected Sandinista officials, but their military leadership still consists predominantly of old Somoza loyalists. Recent intelligence summaries provided to Congress put contra troop strength between 15,000 and 18,000, of whom a small fraction are inside Nicaragua.

*The military threat: Nicaragua's "first target is Nicaragua's neighbors . . . the Nicaraguan military machine is more powerful than all its neighbors combined," Reagan said.

That careful wording seemed to suggest a Sandinista military invasion without flatly declaring it. Reagan also made skillful use of the language of possibility to describe a reddening Western Hemisphere. With Nicaragua as a base, the Soviets and Cubans "can become" the region's dominant power, and then "will be in a position to" threaten U.S. interests and "ultimately" Mexico. "Should that happen," millions of people would flee north, he said.

However, none of Nicaragua's neighbors has expressed concern over any Sandinista invasion, nor have administration officials called that a threat. They worry instead about infiltration of guerrilla trainers but admit that guerrillas move freely worldwide and do not require Nicaragua as a base.

On other occasions, Reagan has displayed pictures of a hemisphere glowing blue with the spread of democratically elected governments.

*The global network of communism: Reagan placed "thousands of Cuban military advisers, contingents of Soviets and East Germans and all the elements of international terror -- from the Palestine Liberation Organization to Italy's Red Brigades" in Nicaragua. He warned not only against "a second Cuba" but "a second Libya" in the region, and evoked Yasser Arafat, Muammar Qaddafi and the Ayatollah Ruhollah Khomeini in addition to the Warsaw Pact as enemies of the contra aid package.

"Now, we must make our decision," he said.

Estimates of the number of Cuban military advisers range from the Sandinistas' count of 200 to the administration's charge that all the Cuban construction workers, teachers and agricultural workers in Nicaragua are also military trainers. While the PLO has an office in Nicaragua and international criminals have been seen in Managua, the administration has cited only secret sources for its allegations that "terrorist training camps" exist in Nicaragua.

The drug connection: A 1982 photograph of Federico Vaughn, an aide to Sandinista Interior Minister Tomas Borge, "loading an aircraft with illegal narcotics, bound for the United States," means that "top Nicaraguan officials are deeply involved in drug trafficking," Reagan said.

But Drug Enforcement Administration spokesman Cornelius Dougherty said earlier this year that "no evidence was developed to implicate the minister of the interior or other Nicaraguan officials."

*The church connection: Reagan said "the entire Jewish community [was] forced to flee Nicaragua," while the Roman Catholic Church "has been singled out" for persecution, evangelical pastors have been tortured and people cannot "worship freely."

Nicaragua's few Jews closed their synagogue for lack of use, and most who left had backed Somoza. A 1983 State Department inquiry found no evidence of anti-Semitism.

While some Protestants have been harassed or their churches closed, mostly in contested Miskito Indian areas, others operate freely. The tortured pastor Reagan cited was working in the contested zone.

Nicaraguan Cardinal Miguel Obando y Bravo is the leading opposition voice, but Catholics are split on the Sandinistas. U.S. Roman Catholic Church leaders critical of Nicaragua's internal policies are still among the sharpest opponents of aiding the contras.

*The history of negotiations: "Ten times we have met and tried to reason with the Sandinistas. Ten times we were rebuffed," Reagan said. Special negotiator Philip C. Habib's recent trip was the 49th U.S. diplomatic mission to the region, Reagan said Saturday.

Habib did not go to Nicaragua, nor did those on many of the other trips. After bilateral discussions began in mid-1984, the Sandinistas complained that U.S. positions amounted to demands that they leave office, and U.S. officials broke off the talks.