THE MOST URGENT job facing Congress, as it reconvenes today, is to deal with the Carter energy legislation. No doubt many people in Congress had secretly hoped that, during the August recess, the devil might fly away with the whole business. But that did not happen, and Congress returns to find it in the same great disorderly pile of papers in which it had been left a month ago.

The basic design of President Carter's July energy plan is flawed. Congress, quite properly, is not inclined to pass it as it stands. It hooks together a great many ideas of widely varying merit, and the first thing Congress must do is to disentangle them and decide which have to be addressed immediately.

Above all, the windfall profits tax needs to be servered from all the other programs. The administration thought that it was strengthening the package by proposing that the tax finance everything else. But this linkage has only diminished the chance of passage, for the opponents of each section are joining forces to fight the whole thing. The legislation now threatens to slide into the same sort of impasse that seized the last Carter energy program in 1977-78.

Taken separately, the case for a tax on oil production is a strong one. Revenues will rise enormously, in part because of public policy. By announcing an absolute quota for oil imports, Mr. Carter has given the domestic oil producers a degree of protection enjoyed by no other industry. The administration would have been wiser to avoid the slippery concept of a windfall profit and simply put a flat tax on each barrel of oil as it comes out of the well. But by one mechanism or another, an oil tax is fair and necessary.

The other parts of the energy plan shouldn't wait for a resolution of the tax issue-- nor should they depend on the amount of money that the tax raises. Poor families' need for aid, in paying their heating oil bills, requires a response at once from Congress. Winter is after all, on its way. The obvious solution is a system of fuel stamps that, by reason of their close analogy with food stamps, can be put into effect quickly.

Next priority goes to initiatives that will produce the most rapid results in reducing the country's need for oil. Conservation comes first. Industrial conversion to coal is second. Solar energy development is third. All will rapidly repay investments, both public and private, that are made now. There is good reason to begin, on a limited scale, building pilot plants for synthetic fuels.

But the president's proposed Energy Security Corporation, with its $88 billion for synthetics and its heavy insulation from political control, is-- at the least-- questionable. That's the kind of thing that Congress could best put off until after the next election. It is late in the year, and precedence necessarily goes to the legislation that can make a difference in the months and years immediately ahead.