CONGRESS IS RESHAPING President Carter's synthetic fuels plan wisely and well -- which is to say cautiously. The president's July proposal would have started construction of dozens of plants simultaneously, at breakneck speed, to make oil and gas from coal and shale. The goal was the equivalent of 2.5 million barrels of oil a day by 1990, with a federal commitment of $88 billion in loan and price guarantees.

Hardly anyone considers that timetable to be realistic. It takes nearly a decade to build a synthetic fuels plant on the huge scale that the administration envisions, and that target would require over 50 of them. The feat shouldn't even be attempted. The sound course is to make haste slowly, putting up one plant in each of the processes to be used, and gaining experience with it before attempting to build them in multiples.

That is what Congress is now telling the president. For Mr. Carter, who wanted to see a great burst of activity in response to his speech, it is doubtless very frustrating. The Carter proposal is now making its way through the various committees and, although he isn't likely to thank them for it, they are rescuing him from an unnecessarily risky venture.

The Senate Energy Committee immediately divided the president's plan in two. Phase One would include one test of each of the major technologies, at full industrial scale. Phase Two would be the replication of the successes.The committee intends to provide financial support -- up to $20 billion, not $88 billion -- only for the first phase. The Senate Budget Committee immediately agreed. It also set up a task force under Sen. Gary Hart (D-Colo.) to consider the environmental and economic implications of these huge plants; the task force is to report this week.

Meanwhile, the House Budget Committee has accepted the idea of a limited first phase, but has voted to lower the limit to a maximum of $12 billion in loan and price guarantees. Now the Senate Banking Committee has set a further restriction of no more than six coal plants and six shale plants. It's not hard to see where the consensus is going. Exploring the possibilities of synthetic fuels is worthwhile, but the costs and risks will be high. It's necessary not to get overcommitted.

The next big test of American energy policy will arrive in the early 1980s, as the recovery from the current recession gets fully under way. If that recovery once again lifts American oil imports to unprecedented levels, it will once again throw the world into an oil crisis and the United States into a recession -- for the third time since 1973. Synthetics cannot possibly be developed fast enough to help the country avoid that trap. In the very short time available, the only resource that offers any substantial hope is intelligent and persevering conservation.