THE SYNTHETIC fuels bill has now emerged from conference, greatly broadened from the first hasty draft whooped through the House a year ago. It's going to be a useful bill, greatly accelerating this country's hesitant experiments with the industrial chemistry that turns shale and coal into heating oil and gasoline.

The bill shares, of course, the defeat of all other energy legislation of the past decade: it won't make much of a diference very soon. Even if it fulfills its author's highest hopes, the benefits will hardly reach a significant scale until the 1990s. Until then, U.S. oil policy will apparently remain essentially a matter of trusting to OPEC's charity, Saudi Arabiahs stability and the great American tradition of being lucky. This slightly sour observation is offered by way of inoculation, so to speak, against the epidemic of hyperbole that is already emanating from the Capitol. There is talk that Mr. Carter will sign this bill amidst appropriate ceremony on July 4.

But within the limits of present political capacity, the synthetic fuels bills makes several valuable contributions. It is wiser not to get entangled in the long quarrel over how much synthetic oil actually can or can't be produced by 1992. The real necessity now is to get several competing technologies into operation, at full industrial volumes to test the environmental effects and the costs. A good many people -- including, unfortunately, OPEC -- have the idea that the sky's the limit for oil prices. If the synthetics technologies can produce liquid fuel in serious quantities at, say $45 a barrel, that will begin to set a ceiling for the prices that Americans ultimately pay for foreign oil. That's very much worth doing.

The gasohol section of the bill is questionable, but gasohol has become a wildly popular cause in the Corn Belt. It's seen there as a way to raise corn prices. The gasohol program is, at least, modest compared with the backing for synthetics. The reason for that disparity is that a corn-fed alcohol still cuts into the food supply, while a coal-fed synthetics plant does not.

There are also to be solar energy and conservation banks -- misnamed, since they will provide grants, not loans, to homeowners. In principle, you could say that the federal government has no compelling duty to pay people to do things that will save them money. But as a practical matter, it's desirable to speed people up in weatherproofing their houses and to provide markets for the solar equipment now being produced. The country has already wasted enough time in commencing these long, slow changes of habit and method. While this bill won't help greatly fo the present, it is also true that sooner or later the future will be here.