All Aboard for Ho Chi Minh City! Steam-powered trip offers breathtaking scenery and vivid glimpses of war's toll. SPINE-JOLTING RIDE THROUGH VIETNAM

MUCH about Vietnam's railway system is foreign - except the passengers. Train engines are Chinese, American, Indian, French, or Czech. Coal for the steam locomotives comes from Australia. The tracks are Soviet-made.

But no foreigners have been allowed to ride the rails in Vietnam - at least that's been the rule since the end of the war in 1975, when the single track between north and south was finally linked up after a 34-year break and the people from the two halves of Vietnam began to mingle by rail.

But one kindly official let this reporter slip on to the express train that runs between Hanoi and Ho Chi Minh City. Later this year, Vietnam plans to allow foreign tourists to ride the rails - but only in a special tourist coach.

And for good reason, for those who seek comfort more than raw reality. The normal coach is hardly a palace on wheels.

The small compartments hold six fold-up bunks, each made of rigid wood, covered with a bug-infested mat. A six-foot-tall person can not sit up straight. The slim passageways are crowded with tots, pigs, and drunks. The window blinds are slit metal - to stop rocks thrown at passing trains by juveniles.

For the 1,300-mile journey, two classes of cars are available, despite Vietnam's attempt to be a classless society. In the luxury sleeping car, which cost about 50 percent more than the other, the fans and lights work. Food is cooked on board.

In second class, the only luxury is free tea, poured from a small pot on the ledge of each window. Food can be bought from station hawkers, selling anything from warm French bread to dried seahorses.

Price of a second-class ticket on the express, which takes 58 hours and runs twice a day, is equal to about two months of a worker's average wage. The super-express train, which runs twice a week and takes 36 hours, is more than double the price. Both trains are usually filled.

The ride itself is ... well, spine-thumping. That's because the rail bed, which was endlessly bombed and mined during the course of two wars, often undulates. Vietnamese refer to the oscillating bounce of the moving train as ``zap zing.''

Vietnam's mountains drop sharply to the South China Sea, and the train's coastal route provides scenes of massive white dunes, vivid green rice paddies, old granite churches, and giant white statues of Buddha. The most breathtaking passage is over Hai Van, south of Hue, which has one of the world's steepest railway inclines and plenty of dark tunnels.

During the winter, northern Vietnamese men like to wear burgundy berets, a holdover from colonization by France. When they gather on a train, they look like a convention of French poets.

Built by the French, Vietnam's railway saw its first north-south linkup in 1936, only to be severed between 1942 and 1976 because of war. One old French luxury coach has been kept in storage for use ``when conditions call for it,'' one official says.

The north-south train is a great leveler of Vietnam's divided society. It brings communist cadres and the military to the conquered south, and rock music and capitalism to the north. For three months last spring, during a period of famine in the north, a train was needed daily to carry rice from the more fertile south.

For northern Vietnamese, the train ride south is a far cry better than the way they traveled to the war against the United States military - down the long jungle path called the Ho Chi Minh Trail, where two out of three died, mainly from American bombs, officials now say.

Remnants of war are everywhere along the line: abandoned American tanks, houses with bullet holes, battered pillboxes and watchtowers. Many bridges have not been fully restored.

Saddest of all is the war's human damage that is visible by train. One teen-age Amerasian girl, dressed in purple pajamas, sells tea to passengers from trackside. Another girl, an amputee, thrusts a begging cup in the window. And all along the route, grave after grave marks the toll taken by five decades of war.

For rail buffs, the charm lies in Vietnam's continuing use of the old steam locomotives. About 100 of them, mainly Chinese-made, ply only the northern third of Vietnam. The mix of different locomotives, with their belching chimneys of white and black smoke, are a reminder of a period in its history - the late 1950s - when Marxist leaders tried to rapidly industrialize a peasant society to create a worker's paradise. One 1955 postage stamp shows a Chinese locomotive with images of Ho Chi Minh and Mao Tse-tung on the cow-catcher.

Wiser now, the leaders still hold up the train as the symbol of an industrialized nation. The 60,000 rail workers have their own newspaper, and show an affinity with their engines and a companionship with each other.

``We're still a poor country,'' says line inspector Ha Dam An. ``But we've been able to learn the foreign technology of these trains and can keep them running.''