SECRETARY SCHLESINGER offers the cherry prediction that (if present trends continue) the gasoline lines will vanish this summer. In other words, the Carter administration is now counting desperately on increased imports of foreign oil.As Mr. Schlesinger knows all too well, it is mainly American anxiety to buy more foreign oil that is strengthening OPEC's bargaining position. As he also knows only too well, the flow of imports, and the length of the gasoline lines this summer and far beyond, depend on contingencies that are absolutely uncontrollable and unpredictable. Consider this brief and incomplete list:

A. They depend on the course of the Iranian revolution, the various separatist movements in the oil fields and the fighting along the Iraqi border.

B. They depend on the stability of the governments of Saudi Arabia and the smaller Persian Gulf states, and their willingness to keep pumping oil at rates that some of their Arab brothers - heavily armed, and numerous - consider a sell-out to the greedy West.

C. They depend on the continuous and peaceful passage of tankers through the Straits of Hormuz, the narrow passage at the mouth of the Persian Gulf, through which more than half of the world's oil imports move.

D. They depend on the good will of governments like Nigeria's not to punish the United States with the oil weapon for its policies on Rhodesia, and the Middle East and who knows what else.

E. They depend, above all else, on the American motorists' willingness to cut back on gasoline consumption - the only one of all these contingencies that Americans themselves can determine.

A kind of panic seems to have seized the Carter administration, in response to the panic at the filling stations. The administration evidently does not feel itself strong enough to tell the country flatly and consistently that it's going to have to cut down the oil. When Mr. Schlesinger says that the gasoline lines will disappear, people think he's promising them all the gasoline to which they are accustomed. That kind of talk gives the rest of the world a clear impression that the United States, unwilling to bear any degree of shortage, is now frantic for more oil at any price. That's a dangerous impression to leave. It opens the country to every kind of blackmail.

Rather than predicting an early end to the gasoline lines, the Carter administration would do well to stick to the simple truth. It is that the shortage is real, and is going to be with us for a long time; that even the present restricted supply is fragile and vulnerable to many kinds of disruption, and that this country may not necessarily be approaching the end of the squeezes at the filling stations but, perhaps, is only at the beginning.

The administration's responsibility now is to help people speed up the process - harsh, wearing and expensive - of preparing to live with less gasoline. It might begin with the warming that this transition is not optional.