Two days after the House fitfully voted down all aid to the Nicaraguan counterrevolutionaries (contras), Alfonso Robelo, a contra leader, threw down the gauntlet to the opposition, specifically the chairman of the House Foreign Affairs subcommittee responsible for Latin American matters, Rep. Michael Barnes (D-Md.). House leaders now have a "challenge," to bring the Sandinistas to the bargaining table, Robelo told a press conference.

In fact, Barnes had already taken up the challenge. Right after the vote he had set up a meeting in his office with the Nicaraguan ambassador to Washington. Barnes laid down three demands: lift censorship; grant Robelo and another contra leader, Arturo Cruz, safe passage back to Nicaragua and the right to state their case; announce a readiness to negotiate regional safeguards with the so-called Contadora Group.

The ambassador would see what he could do. But there were rumors of a U.S. economic embargo on Nicaragua. If that happened, he told Barnes, "we can't do anything." Sure enough, President Reagan slapped on the embargo as his way of replacing the pressure the House vote had removed. In so doing, Barnes insists, the administration "undermined every hope there was."

Barnes makes no brief for the performance of the House and still less for Nicaraguan President Daniel Ortega's arrival in Moscow two days after the House vote -- "It was a slap in the face." But he and others of like mind would argue that Ortega went to Moscow for money and almost certainly not on two days' notice. Whatever, Ortega's untimely trip gives wobbly "moderate" Democrats in the House a handy excuse -- with an eye to next year's congressional election -- for ridding themselves of the political onus of undercutting the president.

But a reversal of last month's vote would do little to settle the real issue, which turns on realizable ends and realistic means.

The administration thinks -- or says it thinks -- that the pressures of aid to the contras and an economic embargo will cause the Sandinistas to put their rule on the line in free elections, abandon their Marxist-Leninist beliefs, stop being a Soviet-Cuban surrogate, forgo external adventures. All this, and more, Secretary of State George Shultz laid down as the administration's terms in a speech on the eve of the House vote.

Yet in the same speech, Shultz pointedly questioned whether "the Sandinistas (can) be trusted to abide by what they agreed to" -- just one more suggestion that the administration does not see a future for Nicaragua with the Sandinistas in charge.

The other side of the argument begins with the assumption that the leverage the administration has at hand or is willing to use is not going to topple the Sandinista regime -- or, more to the point, cause it to change its ideological spots.

Their point is that the Sandinistas are nationalists as well as Marxist- Leninists. If that squares oddly with their heavy Cuban/Soviet dependence, there's less contradiction than meets the eye. Nationalist, in this sense, means not "saying uncle" under pressure, the more so when the "uncle" in question is Uncle Sam.

Witness the history of U.S. relations with Fidel Castro's Cuba. The United States clamped an economic embargo on Cuba 25 years ago.

One result was economic hardship for Cuba, and increased upkeep costs for the Soviets. But Cuba's role in Nicaragua and Grenada -- not to mention its extensive troop deployments in Africa -- hardly suggests a loss of influence.

This is not an argument that "another Cuba," on the mainland, holds no threat. What Barnes and company are saying is that, in fixing objectives, hard-headed distinctions need to be made between an intolerable external threat and what is reprehensible internally -- but beyond this country's reach. That's the blur in the Reagan policy that is getting in the way of sensible debate on what the United States should or shouldn't be doing in Nicaragua.