NOW, HOLD ON just a minute. President Carter and Congress are ready to go galloping off on a multi-multi-billion dollar strategy for manufacturing oil and gas from coal. They are getting themselves prematurely committed to a crash program to build a vast system of synthetic fuels plants. A letter from Rep. Samuel S. Stratton (D-N.Y.) appears on this page today, reflecting the prevailing spirit and denouncing the doubts that have occasionally appeared here. But the present possibilites of the synthetics are sharply limited.

There's strong case for building pilot plants to test and demonstrate the synthetic technologies on an industrial scale.But there's no case for building a lot of similar plants simultaneously and attempting to get into massive production fast by skipping the development phase.

There are several kinds of questions that the first pilot plants will have to resolve. While synthetic fuel plants are now operating in several other countries, none of them is nearly as big as those that the federal government is now considering. To increase scale, in one huge jump, is no simple matter. Nor can anyone be sure about the environmental effects. These processes are sensitive to the types of coal fed into them. Pollution measurements taken at a small German plant using European coal will not necessarily provide a useful guide to the performance of a large American plant using Appalachian coal.

And then there is the matter of cost. Estimates of production costs are hotly debated among the specialists, and the only way to settle the argument is to build and run a plant. If the country now undertakes a large number of first-generation plants together, there will be no opportunity to take advantage of that experience. A crash program risks locking the country into expensive mistakes.

The sheer cost and complexity of the undertaking makes it unlikely that coal-based synthetics can be produced in any significant volume before the 1990s. To attempt to force the pace will threaten to divert resources -- skilled labor, equipment and money -- away from the conventional drilling and mining that is a much better bet for the near term. Oil and gas from coal are possibilities that deserve vigorous development. But for the decade immediately ahead, this country's energy balance will depend less on synthetic fuels than on simple conservation.