PITY THE president, who's off today for five days in Brazil, Colombia, Costa Rica and Honduras. When he stays away from Latin America, he's accused of neglecting a vital region. When he does go, he's accused--are you ready for this?--of promoting his own policy. It dismays some critics, for instance, that he will make an appearance in Central America in support of friendly governments. It's regrettable that presidential visits to Latin America are so few and Latins so sensitive to the symbolism of them that Mr. Reagan can't simply head south and do business. But it's good that he's going all the same.

The "easy" part of the trip will be to salute the various national political evolutions that add up in administration eyes to the hemisphere's current "democratic momentum" -- in the four countries the president is visiting and, much more crudely and partially, in El Salvador and Guatemala, whose presidents he will meet along the way. It is a ragged and incomplete trend, but one worthy of whatever impetus Mr. Reagan can add to it. The longtime democrats in Costa Rica aside, his Central American interlocutors represent conservative, heavily military governments that are being called upon to promote social change and to fight insurgents at the same time. All of Latin America will be listening closely to the way Mr. Reagan addresses these two missions.

The long-term battle for Latin America will be fought, however, on different and even more difficult terrain. In the 20 years since the Alliance for Progress, Latin America has recorded impressive economic growth--6 percent a year in real terms, Secretary of State George Shultz recently observed. To consolidate and sustain these gains, however, and to pay the eye-popping debts whose servicing is a necessary condition of further loans, the region now needs immense infusions of capital. The political disputes -- in Central America, in the Falklands -- may steal the headlines. The continuing effort of Latin America and the Caribbean region to acquire capital, by trade, credits and loans, is unavoidably the hemisphere's abiding concern.

Defying some of its press notices, the Reagan administration has sought to be more attentive in word and, increasingly, in deed to these Latin priorities. Secretary Shultz's economic interest and his commitment to the anti-protectionist cause are especially relevant. Congress could help substantially at this moment by approving the tariff and investment incentives in the administration's Caribbean Basin Initiative.