Amtrak got a tenuous new lease on life this week when its board of directors reluctantly but wisely agreed to abandon a few poorly patronized routes and reduce service on some others.

But the long-range future still looks grim despite a White House decision to continue subsidies at a reduced level in the face of objections from its budget agency, which wants to cut off all federal aid to Amtrak.The trouble is that a surviving but weaker Amtrak will leave the country with an overall transportation system that is not as well-balanced as it can and should be.

Unhappily, the current prospect of a $195 million deficit in fiscal 1995 is just the latest part of a continuing pattern. The U.S. government-run passenger train service has been a consistent money-loser since it was started in 1971.

Though U.S. passenger train travel is up 50 percent over the past decade, Amtrak faces a grim future because of recent accidents, schedule delays produced by deteriorating equipment, and the lingering effects of flood damage a year ago and the brutal winter of 1993-94.

But it doesn't necessarily follow that drastic surgery or even total annihilation is the proper response even though some members of Congress have been leaning strongly in that direction.

If oil and gasoline prices soar in response to natural shortages or another Arab petroleum embargo, the private passenger car could become much less attractive. In that event, America will need at least a basic network of passenger railroad service even more than it does now.

Even if automotive fuel remains plentiful and relatively cheap, the fact that passenger trains are making a comeback in many parts of Europe and Asia should tell this nation's lawmakers something about the wisdom of keeping Amtrak going.

The revival of passenger trains abroad is propelled by the steady worsening of air quality and traffic congestion. America is not immune from those unhappy trends.

Passenger trains can and should be the wave of the future because two railroad tracks can carry as many passengers in an hour as a 16-lane highway. Moreover, compare Chicago's sprawling O'Hare Airport - the world's busiest, handling 60 million passengers a year - with Saint Lazare train station in Paris, which handles more than twice that number in a fraction of the space.

Why not sell Amtrak to some private company or conglomerate of companies? Because most passenger train operations in the United States were abandoned long ago by private owners who are not likely to resume them.

What about the federal subsidies that Amtrak requires? Isn't this constant drain on the taxpayers sufficient reason to call a halt? Not necessarily. The fact is that the United States subsidizes all forms of transportation. There's no reason to make an exception in this case.

Maybe a bigger part of the burden could be shouldered by state governments, which are in much better financial condition than the federal government. Maybe Amtrak could increase its ticket prices. Maybe it could phase out the least-used parts of the passenger network.

In any event, if America is to have a balanced transportation system, it must retain and even strengthen passenger train service. To that end, how about earmarking a cent a gallon from the federal tax on gasoline to create a trust fund for Amtrak operations and improvements? The motorists who pay that tax stand to gain in the long run since increased patronage of passenger trains can mean less congested highways and cleaner air to breathe.