THE BAKER PLAN for the developing countries' debts is still alive, and still valid. Some of the Latin governments have been complaining that there's not enough money in it, and some of the American bankers object that it's moving too slowly. But it continues to be the only sensible way to handle the debts -- the only way that is consistent with prosperity in the indebted countries.

The plan was never a precise and detailed blueprint. The essence of it is a bargain. If the indebted countries undertake reforms that will speed up the growth of their economies, the lenders -- the World Bank and the commercial banks -- will continue to help them. Neither side of the bargain is going to be easy. Some of the commercial banks want to get out of Latin America, and, as for the Latin governments, reform means unpleasant things such as balancing budgets and curbing the patronage that helps governments stay in power.

But the alternative is to default on the debts. That would be a disaster for everyone involved -- for the lenders, obviously, but even more so for the borrowers. It means the paralysis of trade. That's why it hasn't happened on any significant scale. A country that defaulted would find its exports constantly under legal attack throughout most of the world, with not only shipments of goods attached by creditors but the ships and planes carrying those goods as well. While debts pushed most of the Latin economies into recession in 1982, most of them are growing again now. Default promises something far worse, and more enduring.

To advance the Baker plan, there are no doubt many things that Americans could usefully do -- and one of them is to stop calling it the Baker plan. True, it was proposed last October by the American secretary of the Treasury, James A. Baker. That demonstration of support was essential then. But Latin governments understandably dislike the impression that a specifically American plan is being imposed upon them. The implication is unfair, but it makes trouble for them in their domestic politics. At this stage the Americans need to think of ways to broaden the authorship -- in their own interest as well as their partners' -- to make it less distinctively American.

The Reagan administration also needs to make up its mind about the next president for the World Bank. It has a crucial part to play; unlike the commercial banks, it can require economic reforms as the condition of its loans. The current president, A. W. Clausen, leaves in June and, in the absence of a successor, the bank is suffering a visible loss of momentum. The politics of the Latin debts is complex, and some of the delays in fashioning remedies are inevitable. This one is not. The White House is procrastinating.