WHEN PRESIDENT CARTER first began to bring out his energy policy last month, some of the key numbers were left until later. They turned up a couple of weeks ago in the back of the little book entitled "The National Energy Plan" that the White House has been distributing. An illuminating table there shows how much energy the country would be using in 1985 under this plan, and which fuels. Those numbers imply a gap in the plan. The country can't get there from here. Either the plan must be augmented or oil imports will be well above 7 million barrels a day by the mid-1980s.

That gap is not small. Hans Landsberg, an economist with long experience in this field, offers an estimate in the analysis that we print today on the opposite page. As he points out, coal production and use are unrealistically high. The projection for nuclear power also seems too high, in view of the extremely long lead times that reactors require. But it's slow work to develop any major source of energy, and there won't be any new ones available in 1985 that are not visible today. A spectacular new oil strike, for example, is always a possibility. But it was nine years ago that oil was discovered on the North Slope of Alaska, and that oil won't begin to reach consumers until this winter.

Closing the gap means either reducing the demand for energy or increasing oil impports beyond the plan's target. The administration has taken an extremely cautious approach to conservation because it fears doing damage to the economy. It is trying to stay far away from anything that might threaten to depress automobile sales, or disrupt the housing industry, or curtail industrial expansion. It's correct to say that conservation can be accomplished without destroying jobs - if it's done carefully, at a certain pace. But if the pace is forced beyond limits that are not yet entirely clear, unemployment rises.

The alternative is, unfortunately, more foreign oil. That's the choice that Dr. Landsberg recommends. But there are large risks in that one as well - even with the strategic oil storage that, incidentally, the country has not yet begun to accumulate. Even if that oil keeps pouring in without interruption, rising American demand would keep the world oil market tight enough to encourage further OPEC price increases. Over the next decade, OpEC is likely to do more than Congress to restrain American energy imports.

The President's plan is valuable, but incomplete. It has given direction to the formless debate over energy that has been going languidly along ever since the embargo three years ago. It has put the country on a fairly well-marked track of modest conservation and substantial increases in energy supplies. But for all of the President's speeches on the subject, the country still hasn't seen the full strategy. It looks as though the President set his goals and then drew back from some of the implications, papering them over with excessively optimistic forecasts for coal and nuclear power. As the country goes through the next several years, experience will not doubt show the need for further restraints. The present energy plan is not a completed blueprint. It merely indicates a course to be followed - with further implementation to come over the years.