LAST WEDENESDAY MORNING, Secretary of Transportation Brock Adams announced his proposal to cut almost in half the nation's railroad passenger network. On Wednesday evening, the Southern Crescent pulled out of Union Station here for the last time under the auspices of the Southern Railway-so much for riding the rails in style. The government, like the railorad corporations before it, has become convinced that most long-haul passenger trains deserve to live only in memories.

The evidence that Secretary Adams put forward to justify this dismembering of Amtrak is substantial. A 43 percent cut in the length of the network its trains serve will reduce the number of passengers it carries by only 9 percent and will save the nation's taxpayers about $1.4 billion in five years.

Regardless of how you feel about the particular train service that Mr. Adams has marked down for extinction, those numbers are too impressive to ignore. So are some other facts about Amtrak's operations. Amtrak collects from its customers only 37 cents for every dollar it spends; the other 63 cents come from the government. On some routes, it could come from the government. On some routes, it could save money by giving its passengers airline tickets instead of putting them on its trains. Its annual deficit has grown from $150 million to $575 million in six years:

No doubt there will be considerable anguish, both on Capitol Hill and elsewhere, over the specific cuts Mr. Adams has proposed. He wants to lop off all the routes Amtrak was forced to serve for purely political reasons, as well as many other routes that were picked on their merits. The network he proposes to retain is less than a skeleton of what once existed. Only on the East Coast and, to a lesser extent, in the area around Chicago will anything remain that deserves to be called a passenger railroad system.

We were among those who, at the beginning of this decade, urged the government to create Amtrak as a way of preserving a national passenger-train network. The railroads, with a few exceptions, had been killing passenger service through neglect. The idea that a well-planned system with good management and good service would attact enough travelers back to the rails seemed to us at least worth a try.

And Amtrak, for all its shortcomings, has tried, but outside of the Boston to Washington corridor, where the revival of the trains has been remarkable, the experiment hasn't worked. The lure of the airplane for business travelers and of the automobile for vacationers has been too great. For us, the evidence that Amtrak needed drastic surgery became overwhelming when the Southern Railway, which had refused to join Amtrak and insisted upon running its own train, finally gave up. Seven million dollars a year was more than it was willing to spend to keep the Crescent, its pride and joy for more than 80 years, on the tracks.

Congress may wish to make some minor changes in the proposal Secretary Adams is sending to it, but it should not make many. The surprise is not that he wants to cut Amtrak so sharply but that he is willing to leave so much of it in operation. Long-haul passengers trains may be energy efficient, useful to have around in case of an emergency, and fun to ride. But so are horses. Without travelers who want to use them, both modes of transportation have become expendable on a national long-distance scale.