The steamy little rally held by supporters of contra aid under White House auspices only served to make a point well known: that the enterprise has the fervent support of Cuban Americans.

The conversation among the sweltering crowd of 3,000 that had been bused in from New York and New Jersey was almost exclusively in Spanish, and the speakers, except for the president's communications director, Patrick J. Buchanan, were bilingual. He was rather restrained in his remarks, praising the contras as "the greatest peasant army ever raised in Central America" and promising that in Congress, "the tide is with us."

The tide in the country, however, has never turned. In 1983, surveys showed 63 percent opposed (28 percent for) intervention in Nicaragua. A poll taken this spring showed exactly the same returns. The sombrero-set may be all for it, but the public is not buying.

President Reagan tells them Nicaragua is another Cuba, another Libya, a Soviet base. They look at it and see another Vietnam.

Former U.N. ambassador Jeane J. Kirpatrick, a preeminent contra booster, was the darling of the crowd, greeted with great yelps and cheers by the sweating, mostly middle-aged demonstrators. She was introduced in a full-throated roar by Col. Sam Dickens of the American Security Council, and spoke at the top of her voice in Spanish for 10 minutes. She switched to English for a report on Soviet-Cuban perfidy; in neither language did it seem her heart was in her work. Maybe it was the heat.

Assistant Secretary of State for Inter-American Affairs Elliott Abrams read a greeting in Spanish from Reagan, who was at Camp David for the weekend, and was spared the sight of for-once welcome demonstrators in Lafayette Park. (In Richard Nixon's day, the presence of a single dissident was enough to immobilize the leader of the Western world.)

Rep. Robert K. Dornan (R-Calif.) hoarsely relived D-Day, and had a laborious time working his way back to Nicaragua. At one point he quoted John F. Kennedy's "I Am a Berliner" to reinforce the "I Am a Contra" theme proclaimed on T-shirts and stickers pasted on Spanish-language banners.

The speakers may have been a little frustrated. They thumped away at Fidel Castro, the devil incarnate to the group at hand. They probably would have preferred to dump on the House Democrats who have retreated but have not yet surrendered in the war with Reagan on contra aid. The Democrats got off easy because the illusion that the contras have "bipartisan" support is being floated. Previously, Buchanan charged dissidents with being for Daniel Ortega, president of Nicaragua.

Since the House vote on April 16, when the Republicans outsmarted themselves by voting for a Democratic amendment that would have banned all aid, the administration has scored only one success.

It beat back a peace scare. The Contadora countries had produced a regional peace treaty, which to the horror of the White House seemed likely to be signed by all involved, including Nicaragua, by June 5.

A New York Times headline reflected the consternation: "Pentagon Predicts Big War if Latins Sign Peace Accords."

The Defense Department was simply rephrasing its old argument that if we don't arm the contras, we will eventually have to send in the Marines to keep the rampant Sandinistas from turning the neighborhood into what Reagan called "a sea of red, lapping at our shores" -- although the Pentagon is adamant about not fighting another war without popular support.

The State Department rushed out to deny the Pentagon assessment, but was hideously embarrassed that Philip C. Habib, the veteran trouble-shooter dispatched by the president to find a negotiated settlement, had actually come close to it. A nameless official spokesman operating out of the White House trashed Habib as "imprecise" and "in error." The president of Honduras was hauled up to Washington to say that contra aid is vital.

A strenuous program for rehabilitating the contra leadership was initiated. After a series of meetings, the three civilians supposedly in charge were given a fighting chance to overrule the ex-Somocista military commanders, who have given the cause a bad name by misappropriating funds, running drugs and shooting up peasant villages.

The president made another speech about Soviet arms shipments to Nicaragua, hoping, presumably, that they will be more dependable than the MIGs that turned up, although not for long, several years ago.

Republicans and Democrats, meanwhile, paid court to Rep. Dave McCurdy (D-Okla.), who bailed out Reagan last year with a bill to give $27 million in "humanitarian" aid and is presumably fashioning legislation that will again soothe nervous Democrats who look at 3,000 Cuban Americans in Lafayette Park and multiply it into a vengeful multitude.