THE STRUGGLE over the Nicaraguan contras is being renewed, at the lower pitch befitting the anticlimactic nature of this phase, on the issue of humanitarian aid. The administration's approach is consistent with its familiar goal of forcing the Sandinistas out of power. It sees humanitarian aid as essential to holding the contras intact, if not as a fighting force, then as a bargaining force. It favors a broad definition of ''humanitarian'' (to include supplies still in the old military aid pipeline), believing that under a strict food-and-medicine definition rebels become merely refugees. It insists on keeping delivery in American hands on grounds that putting delivery under international auspices cuts off or at least attenuates the contras' Washington backing.

On humanitarian aid, Speaker Jim Wright calls for bipartisan agreement, by which he appears here to mean administration approval of a House position. But he is still working on composing a House position. Among the Democrats are some who would dissolve the contras immediately -- even though the Sandinistas themselves say they are willing to wait for some months. Other Democrats, who felt that contras fighting in the battlefield would not make the Sandinistas more democratic, suggest now that contras resting in cease-fire locations would. Meanwhile, Republicans warn they will not support humanitarian aid that comes in the form of a Democratic ''surrender package.''

We think humanitarian aid can give a small but real bargaining lift to the contras, who are at this moment trying to negotiate what passage is still available to them from civil war to pluralism. The package should be generous, broadly defined and American delivered; it could also be internationally inspected.

A heavy obligation rests on anticontra Democrats to lean politically on the Sandinistas -- not only in the humanitarian aid vote but also by their calls to Managua. Why do so few of them reinforce Oscar Arias' repeated and vigorous demands that the Sandinistas make good on their pledges to democratize? Speaker Wright's last initiative in this area was in 1984. Democrats hold back on criticizing the Sandinistas in evident fear of bolstering President Reagan's appeals for the rebels. They say ''give peace a chance'' as though the words were self-fulfilling and as though democracy were not essential to secure peace. The impression is left that protecting Democrats in Congress is more important than protecting democrats in Central America.