THE ARIAS-Reagan-Ortega policy for Central America, which is what it is, is lurching forward. President Arias of Costa Rica devised the basic plan, which in its salient aspect calls for Nicaragua to democratize and the United States simultaneously to cut off the contras. Nicaragua has been responding and taking steps toward democracy. In turn, the United States falls under an obligation to match Nicaragua's progress by defunding the contras in a manner proportional to the Sandinistas' own progress.

Abandoning earlier thoughts of requesting a large aid package for a long period, Mr. Reagan yesterday asked for a small package for a short period. Nine-tenths of the $36 million request would go for food and the like plus -- and here Congress may stiffen -- so-called nonlethal military supplies and transport. The tenth of it earmarked for arms would be put in an escrow account and released on March 31 only after the president had consulted with the Central American presidents, reported publicly on these consultations and certified that Nicaragua had not complied with the peace plan. In these two months, efforts would presumably go forward to arrange a cease-fire and test and confirm the political opening offered by the Sandinistas.

Two considerations count here: the first is that pressure works. It doesn't work by itself, as Mr. Reagan proved by applying contra pressure for six years without results, but it works when there is a peace plan to relieve the pressure. It would be disastrous to apply so much pressure that the plan buckled, but that does not seem to be happening. On the contrary, the Sandinistas, in the same conditions of pressure and diplomacy that Mr. Reagan would now continue for a few more months, have been coming along.

Then, Mr. Reagan surely would have preferred giving himself sole unchecked power to determine release of the military money, but he figured Congress would not go along. Instead, he took into account Speaker Jim Wright's proposal to let the five Central American presidents decide by promising to ''personally consult'' with those presidents. Legislators who don't trust Mr. Reagan may feel obliged to vote against his aid request. But we think a president who will have to keep dealing with Congress and Central America on Nicaragua for a whole further year would be foolish and unlikely to cheat.