The house is to vote again today on Nicaragua, and again a close vote is expected. That is the striking thing about the issue of aiding the anticommunist resistance. The argument, now in its fifth year, has become a fixture of the Reagan presidency, an emblem at once of the president's intense determination and of his intense frustration. Each side plays a guerrilla game, refusing to accept any one battle's outcome as conclusive, keeping the struggle going, hoping somehow to prevail.

Unsurprisingly, the Washington argument has taken on a political tinge. Unable to persuade a reliable congressional majority that its policy is compelling, the administration has sought to raise the political costs to those who see Nicaragua another way. Its effort has had a part in inducing some Democrats, constituting a swing bloc, to temper their party's general wariness of even indirect military involvement with a conditional readiness to offer military aid. Still, as the president reiterated yesterday, the administration finds the conditions onerous.

Almost lost sight of in the smoke of argument in Washington is the fire of battle in Nicaragua. The Nicaraguan contras can punish the Managua regime and make it bleed, but familiar and continuing restraints -- including not only American ambivalence but also their own continuing problems of organization and leadership -- make them an unlikely instrument of the administration's liberating purposes. The Sandinistas have indeed gone back on the promises of their revolution of 1979, but they have also had nearly seven years -- including five-plus Reagan years -- to consolidate power. American sponsorship of the contras has no doubt gratified some Nicaraguans, but it has made others sympathetic to the Sandinistas' claim to be nationalists repelling yet another Yankee intervention.

The Contadora ''process'' has been a great disappointment, though it has to be acknowledged that its task -- to reconcile the Sandinistas' intent to preserve their power with the Reagan administration's effort to install democracy -- is daunting. Nonetheless, there is value in a continuing attempt by the democracies of Latin America to lower the level of violence in Central America and to raise the level of political tolerance in Nicaragua. In the current circumstances, violence is going up and tolerance down.

Meanwhile, the United States has important work to do in Central America: to ensure that Nicaragua not become a strategic base or a threat to its neighbors, and to support and strengthen the countries in the region that are trying to build democracy. These are the lines of policy on which the president and Congress can surely agree